MICROELECTRODE FOR INSERTION INTO SOFT TISSUE

Abstract

A microelectrode that is useful for implantation into, or placement adjacent, soft tissue, such as neural tissue, and includes a conductive element having a distal non-insulated portion and a proximal insulated portion. Part of the conductive element is disposed in a casing of electrically insulating non-degradable material, the casing encapsulating the non-insulated portion of the conductive element, and including at least one opening and a first structural component in which the electrically insulated portion of the conductive element can slide in an axial direction.

Claims

1-60. (canceled)

61. A microelectrode configured to be at least partially embedded into or at least partially placed adjacent to soft tissue, in particular nervous, endocrine and muscle tissue, comprising an elongated electrically conductive element, the elongated electrically conductive element comprising a proximal electrically insulated portion and distal non-insulated portion, at least part of the conductive element being disposed in a casing (envelope) of electrically insulating non-degradable material, wherein the non-insulated portion of the element is encapsulated (surrounded) by the casing forming a distal chamber, in which the conductive element can slide in an axial direction, the casing of the distal chamber having at least one opening providing (after implantation) a fluidic electrically conductive bridge between the non-insulated portion of the conductive element and the soft tissue enabling an exchange of ions between the distal chamber and the tissue, wherein the at least one opening is useful for recording and stimulation of electrically excitable cells, wherein the casing comprises a first structural component in which the electrically insulated portion of the conductive element can slide in an axial direction.

62. The microelectrode according to claim 61, wherein the first structural component partitions the casing (envelope) into a distal chamber and a proximal compartment.

63. The microelectrode according to claim 61, wherein at least part of the electrically insulated portion is localized within the distal chamber.

64. The microelectrode according to claim 61, wherein a lumen/void (enabling axial movements) is provided between the first structural component and the electrically insulated portion of the conductive element

65. The microelectrode according to claim 61, wherein the innermost material(s) of the casing and/or the first structural components and/or the outermost material of the proximal electrically insulated portion of the element is/are (each) selected to reduce friction.

66. The microelectrode according to claim 61, wherein the distal chamber comprises a second structural component configured to reducing radial movement of the non-insulated portion of the conductive element relative to the distal casing, while also being configured to enable an axial movement of the non-isolated conductive element with respect to the second structural component.

67. The microelectrode according to claim 61, wherein the perpendicular distance between the non-insulated portion of the conductive element and the at least one opening in the casing of the distal chamber remains essentially the same during axial movements of the casing relative to the conductive element, optionally the perpendicular distance not changing more than 20%.

68. The microelectrode according to claim 61, wherein the at least one opening has an area of at least about 1 μm2.

69. The microelectrode according to claim 61, wherein the distal chamber comprises a plurality of openings in the distal casing.

70. The microelectrode according to claim 61, wherein the distal portion of the casing of the distal chamber has a three-dimensional shape narrowing in distal direction such as a spherical shape.

71. The microelectrode according to claim 61, wherein a proximal portion of the distal chamber narrows down, preferably exhibiting an annular form forming the first structural component, in which the electrically insulated portion of the conductive element can slide in an axial direction.

72. The microelectrode according to claim 61, wherein the friction between the casing and the adjacent soft tissue is higher that the friction between the innermost material of the casing and/or the first structural component and/or the outermost material of the proximal electrically insulated portion of the element.

73. The microelectrode according to claim 61, wherein the outermost material and/or outermost surface structure of the casing is selected to increase friction against the soft tissue.

74. The microelectrode according to claim 61, wherein the casing of the distal chamber comprises an engagement element configured to reversibly engage with an elongated rigid pin such as a needle, the pin being configured to insert the microelectrode into the soft tissue or placing the microelectrode adjacent to soft tissue, the engagement element comprised at the distal portion of the distal chamber.

75. The microelectrode according to claim 74, wherein the engagement element is a loop or net comprising micro- or nanofibers

76. The microelectrode according to claim 74, wherein the engagement element is degradable in body fluids.

77. The microelectrode according to claim 61, wherein the casing comprises means for increasing friction between the casing and the adjacent soft tissue.

78. The microelectrode according to claim 77, wherein the means for increasing friction is selected from micro- or nano-fibers attached to the outermost surface of the casing.

79. The microelectrode according to claim 61, wherein a void/lumen between the first structural element and the outermost layer of the proximal electrically insulated portion of the conductive element comprises a composition facilitating the movement of the first structural element with respect to the outermost layer, particularly a composition comprising any one of lipids, hyaluronic acid, silicones (such as silicone oil or silicone grease) and a polymer of monosaccharides such as glucose and combinations thereof.

80. The microelectrode according to claim 61, wherein the casing has a rotationally symmetric shape, suitably cylindrical shape.

81. The microelectrode according to claim 62, wherein the diameter of the proximal compartment widens in a proximal direction.

82. The microelectrode according to claim 61, wherein the distal chamber and optionally the proximal compartment comprises at least one biologically active substance such as a pharmaceutically active substance.

83. The microelectrode according to claim 61, wherein the conductive element extending proximally of the proximal compartment is of a material or of materials different from that or those of the conductive element disposed in the proximal and distal compartments.

84. The microelectrode according to claim 61, wherein the electrically insulating material of the casing is a biocompatible, non-degradable flexible polymeric material, particularly a biocompatible, flexible polymeric selected from polyurethanes, polyethylenes, polymers with a backbone comprising benzene (e.g. parylenes such as Parylene C and Parylene M), and polymers based on the polymerization of tetrafluoroethylene and flexible inorganic materials (such as glass or glass-like materials)

85. The microelectrode according to claim 61, wherein the distal chamber, and optionally the proximal compartment, comprises a biocompatible material dissolvable or degradable in aqueous body fluids and providing structural support to the microelectrode when dry.

86. A microelectrode probe comprising a microelectrode as defined by claim 61, wherein the distal chamber, and optionally the proximal compartment, comprise(s) a biocompatible material providing structural support to the probe when dry for insertion into soft tissue, wherein the biocompatible material is dissolvable or degradable in aqueous body fluids.

87. The microelectrode according to claim 61, wherein the microelectrode or microelectrode probe is embedded in an embedding matrix of a biocompatible material providing sufficient rigidity to the probe when dry for insertion into soft tissue and dissolvable or degradable in aqueous body fluids.

88. The microelectrode according to claim 61, further comprising an element holder, the electrically conductive element extending (in proximal direction) through the element holder, the holder configured to be secured to a tissue different from the soft tissue, in particular osseous or connective tissue.

89. The microelectrode according to claim 61, wherein the electrically conductive element is in electrical engagement with an apparatus for registration of biological signals and stimulation of soft tissue.

90. The microelectrode according to claim 61, wherein the biocompatible matrix-materials are selected from carbohydrate-based materials, protein-based materials, and non-natural polymeric materials, and mixtures thereof.

91. A first array of microelectrodes according to claim 61, wherein the microelectrodes are adhesively attached to micro or nanofibers.

92. The first array according to claim 91, wherein the microfibers are degradable.

93. A second array of microelectrodes according to claim 61 partially or entirely embedded in an array matrix of a biocompatible material providing sufficient rigidity to the array when dry for insertion into soft tissue and dissolvable or degradable in aqueous body fluids.

94. The microelectrode according to claim 61, wherein the biocompatible dissolvable or degradable materials are selected from carbohydrate-based materials, protein-based materials, and non-natural polymeric materials, and mixtures thereof.

95. The second array according to claim 93, further comprising an array cover.

96. The second array according to claim 95, wherein the array matrix extends to the distal face of the array cover.

97. The second array according to claim 93, further comprising an array casing of a flexible, non-degradable material embracing a part of the array matrix.

98. The second array according to claim 97, embedded in an outer array matrix of a biocompatible material which is solid when dry and dissolvable or degradable in aqueous body fluids.

99. The second array according to claim 98, wherein the biocompatible materials are selected from carbohydrate-based materials, protein-based materials, and non-natural polymeric materials, and mixtures.

100. A method for manufacturing the microelectrode according to claim 61, comprising: providing an elongated electrically conductive element; covering a proximal portion of the element with an electrically insulating layer thereby providing a proximal electrically insulated portion and a distal non-insulated portion of the conductive element; forming a distal matrix dissolvable or degradable in aqueous body fluids extending axially around, and optionally extending in a distal direction from the distal non-insulated portion of the conductive element; applying a sliding facilitating composition to a section of the insulated element proximally with respect to the distal matrix and distally with respect to an optional proximal matrix wherein the sliding facilitating composition is facilitating the axial movement of a first layer of electrically insulating non-degradable material of the conductive element, said medium optionally providing for a sufficient void/lumen between the insulating layer of the conductive element and first layer of electrically insulating non-degradable material; optionally forming a proximal matrix extending axially around at least part of the proximal electrically insulated portion of the conductive element; covering the distal matrix and at least part of the proximal electrically insulated portion of the conductive element with a first layer of electrically insulating non-degradable material, thereby providing a casing encapsulating the distal non-insulated portion of the element forming a distal chamber and a first structural element; cutting part of the non-insulated portion of the conductive element and first layer of electrically insulating non-degradable material near the distal end of the distal matrix (distal end of the distal chamber) comprising the distal non-insulated portion of the electrically conductive element, thereby providing a distal opening of the distal compartment; applying a further distal tip matrix distally to the distal opening; and covering the tip matrix and at least part of the first layer with a second layer of electrically insulating non-degradable material, thereby forming a distal end cap part forming part of the casing of the distal chamber, wherein the distal and optionally proximal matrices provide structural support to the microelectrode or probe when dry for insertion into soft tissue, and wherein at least one opening through the first layer and optionally second layer of the casing of the distal chamber is provided.

101. A method for manufacturing the microelectrode according to claim 62, comprising: providing an elongated electrically conductive element; covering a proximal portion of the element with an electrically insulating layer thereby providing a proximal electrically insulated portion and a distal non-insulated portion of the conductive element; forming a distal matrix dissolvable or degradable in aqueous body fluid extending axially around, and optionally extending in a distal direction from the distal non-insulated portion of the conductive element; forming a proximal matrix extending axially around at least part of the proximal electrically insulated portion of the conductive element and thereby forming an intermediate section of the insulated conductive element with an axial extension, the intermediate section positioned proximally to the distal matrix and distally to the proximal matrix not covered by the distal and proximal matrices; applying a thin (up to about 5 μm) layer of a first intermediate matrix and/or sliding facilitating composition to the intermediate section of the insulated element facilitating the axial movement of a first layer of electrically insulating non-degradable material with respect to the insulating layer of the conducting element, said first intermediate matrix and/or composition providing for a sufficient void/lumen (annular channel) between the electrically insulated portion of the conductive element and the first layer of electrically insulating non-degradable material; covering distal, proximal matrices and the intermediate section of the proximal electrically insulated portion of the element, the intermediate section comprising an intermediate matrix and/or sliding facilitating composition, with a first layer of electrically insulating non-degradable material, thereby providing a casing comprising a distal chamber, a first structural element and a proximal compartment; optionally providing a second intermediate matrix on the first layer of electrically insulating non-degradable material in the constriction in radial direction of the first layer between the distal chamber and proximal compartment; cutting part of the distal non-insulated portion of the electrically conductive element and the first layer of electrically insulating material near the distal end of the distal matrix (distal end of the distal chamber), thereby providing a distal opening of the distal chamber; applying a further distal tip matrix distally to the distal opening; covering the distal tip matrix and at least part of the first layer with a second layer of electrically insulating material thereby forming a distal end cap forming part of the casing of the distal chamber; and removing the first layer and optionally second layer at a circumferential annular zone of the proximal matrix, wherein the distal matrix, distal tip matrix, proximal matrix and optionally first and second intermediate matrices are of a biocompatible material providing sufficient rigidity to the probe when dry for insertion into soft tissue and dissolvable or degradable in aqueous body fluids, and wherein at least one opening is provided through the first and optionally second layers of the casing of the distal chamber.

102. A method for manufacturing the microelectrode according to claim 61, comprising: providing an elongated electrically conductive element; covering a proximal portion of the element with an electrically insulating layer thereby providing a proximal electrically insulated portion and a distal non-insulated portion of the element; providing a first structural element configured to enable an axial movement with respect to the proximal electrically insulated portion of the conductive element; positioning the first structural element around the proximal electrically insulated portion of the conductive element, suitably at a certain axial distance from the distal non-insulated portion of the conductive element; optionally applying a proximal matrix dissolvable or degradable in aqueous body fluids around the proximal electrically insulated portion of the conductive element, the proximal matrix extending from the proximal face of the first structural element in proximal direction; applying a distal matrix dissolvable or degradable in aqueous body fluids around the distal non-insulated portion of the element extending from the distal face of the first structural element in distal direction, and extending in a distal direction from the distal non-insulated portion of the conductive element, suitably up to several millimeters; and applying a first layer of electrically insulating non-degradable material on the optional proximal and distal matrices and the circumference of the first structural element, thereby forming a casing comprising a distal chamber and a proximal compartment, wherein at least one opening is provided through the first layer of the casing of the distal chamber.

103. The method according to claim 100, wherein the proximal matrix widens in a proximal direction.

Description

SHORT DESCRIPTION OF THE FIGURES

[0177] FIG. 1 A region of neural tissue for implantation of a microelectrode probe of the invention, in a section perpendicular to a bone protecting the region

[0178] FIG. 2 The region of FIG. 1 after providing a circular hole in the bone, in the same section

[0179] FIG. 3a A schematic representation of a microelectrode probe of the invention in an axial section

[0180] FIG. 3 An electrode according to FIG. 3a immediately upon implantation

[0181] FIG. 4 A microelectrode of the invention with a plurality of openings through the distal chamber

[0182] FIG. 5 A microelectrode of the invention with a distal chamber but without a proximal compartment proximally to the distal chamber

[0183] FIG. 5a A microelectrode of the invention featuring a tubular structure distinct from the casing.

[0184] FIG. 5b A microelectrode of the invention featuring a tubular structure distinct from the casing further comprising a structural element within distal chamber

[0185] FIG. 6-14 A process for the manufacturing of a microelectrode probe of the invention showing consecutive pre-stages to the microelectrode probe illustrated in FIG. 15

[0186] FIG. 15 Microelectrode probe of the invention in axial direction

[0187] FIG. 16 A variety of a microelectrode of the invention comprising an embedding matrix

[0188] FIG. 17 A microelectrode probe of the invention implanted in neural tissue prior to the dissolution of embedding matrix and proximal and distal matrices

[0189] FIG. 18 A proto microelectrode of the invention implanted into neural tissue in a state of partial dissolution of the embedding matrix and in a stage of transformation to a microelectrode of the invention

[0190] FIG. 19 A microelectrode of the invention formed in situ (in situ microelectrode) from the microelectrode probe of FIG. 17

[0191] FIG. 19a A microelectrode of the invention formed in situ (in situ microelectrode) from the microelectrode probe of FIG. 17. The casing has accommodated for spatial movement of the surrounding soft tissue.

[0192] FIG. 20 An array of four microelectrode probes of the invention

[0193] FIG. 21 A tubular cross section of the array through the distal chambers of the microelectrode probes

[0194] FIG. 22 Half mold with tubular structure of a manufacturing step for producing a microelectrode featuring a tubular structure distinct from the casing

[0195] FIG. 23 Tubular structure comprised in variants of the microelectrode

[0196] FIG. 24 A variant of the microelectrode of the invention where the radial extension of the casing of the distal compartment is only marginally wider that the radial extension of the insulated portion of the conductive element.

[0197] FIG. 25 An array of microelectrodes. The individual microelectrodes are held together by a web of micro- or nano-fibers.

[0198] FIG. 26 A microelectrode comprising an engaging element. The casing also exhibits micro- or nano-fibers increasing the friction of the casing with respect to the surrounding soft tissue.

[0199] Several embodiments of the invention are describes in more detail below. The embodiments should not be construed as to limit the general concept of the invention.

DESCRIPTION OF SOME EMBODIMENTS

[0200] Implantation and Tissue Environment Principles.

[0201] FIGS. 1, 2, 3a and 3 illustrate schematically the intersection of a skull without a microelectrode (FIG. 1 and FIG. 2), an implanted microelectrode probe into neural tissue (FIG. 3) and a microelectrode probe (FIG. 3a). The neural tissue (3) here is brain tissue, protected by the skull bone (1) from which it is separated by a thin layer (2) comprising several sub-layers, such as the dura mater, the arachnoid mater, the pia mater and cerebrospinal fluid. The neural tissue (3) is prone to spatial displacement in respect of the skull bone (1) by movements of the head, the displacement schematically depicted in direction parallel with the skull bone (1) (arrows b, b′) and perpendicular direction (arrows a, a′). Tissues (2) intermediate between the skull bone 1 and brain tissue 3 are similarly displaced but not necessarily to the same extent.

[0202] Prior to implantation of a device according to the invention access to a desired position of the brain is provided by drilling a circular hole (8) in the skull (FIG. 2).

[0203] In the next step a device of the invention, such as the microelectrode probe (10) of the invention of FIG. 3 a or a microelectrode probe array, is inserted through the hole (8) into brain tissue (3) (FIG. 3). Upon implantation the microelectrode probe (10) is transformed into a microelectrode (in situ microelectrode) of the invention by contact with aqueous body fluid. The fully functional in situ electrode is formed once the matrix materials have completely dissolved or been degraded. The microelectrode probe (10) comprises a cover (7) anchored in the skull bone at the hole (8) protecting the skull bone and soft tissue. The microelectrode (10) comprises a metallic or other electrically conductive element (6) attached to and penetrating the cover (7), which extends from the proximal face of the cover (7) for electrical communication with a microelectrode control unit (not shown) disposed extracorporeally or implanted under the skin. A proximal portion of the element (6p) is electrically insulated while a distal portion of the conductive element (6p) is non-insulated. A first structural component (12) divides the casing (13) into a proximal compartment (11p) and a distal chamber (11d). The distal chamber is encapsulated by the casing further comprising an opening (14) enabling an electric current to flow between the distal non-insulated portion of the conductive element (6d) and the neural tissue (3). In this microelectrode the first structural element is integrated with casing. The first structural element forms an integral part of the casing. Hence, the casing and the first structural element share the same material. The casing, i.e first structural element, is slidably connected to the proximal insulated portion of the conductive element (6p).

[0204] FIGS. 4, 5, 5a and 5b show three variants of the microelectrode as configurated after complete dissolution of matrices.

[0205] FIG. 4 shows a variant of the microelectrode as configurated after complete dissolution of the matrices of biocompatible material dissolvable or degradable in aqueous body fluids. This variant comprises a proximal (11p) compartment and a distal chamber (11d). Between the proximal compartment and distal chamber a first structural component (12) is present embracing the proximal insulated portion (6p) of the conductive element (6). As seen in FIG. 4 the casing (13) encapsulates the distal chamber (11d). The first structural component (12) embracing the insulated portion of the conductive element (6p) is slidably attached to the outermost layer of the proximal insulated portion of the conductive element. Here, the outermost layer is equivalent to the insulating layer (15) of the proximal portion of the conductive element (6p). Instead of one opening the distal chamber has four openings (14). All four openings are axially positioned such that the perpendicular distance of the distal non-insulated portion of the conductive element (6d) to the openings remains essentially constant when the conductive element (6), i.e. distal non-insulated portion of the conductive element (6d) and proximal insulated portion of the conductive element (6p), moves with respect to the first structural component (12) which coincides with the movement of the conductive element with respect to the casing encapsulating the distal chamber. The distal tip (16) of the non-insulated conductive element should have enough travel distance in axial direction that the tip never penetrates the casing of the distal end cap (17) of the casing of the distal chamber (11d).

[0206] FIG. 5 depicts a microelectrode variant comprising only a distal chamber (11d) encapsulation the distal non-insulated portion (6d) of the conductive element (6). The casing gradually transforms into a first structural element (integrated tubular structure) (12), the first structural element (12) being slidably attached to the proximal electrically insulated portion (6p) of the conductive element. The proximal insulated portion (6p) of the conductive element has an electrically insulating layer (15). The distal compartment comprises an opening (14). The opening (14) is located axially such that the perpendicular distance of the opening (14) with respect to the non-insulated portion of the conductive element (6d) remains essentially constant even if the conductive element (6), i.e. the non-insulated portion of the conductive element (6d), moves in axial direction.

[0207] FIG. 5a shows a variant of the microelectrode comprising a first structural element (29) which does not form part of the casing (material) (31), (32). The first structural element which may be of Teflon® comprises a channel which accommodates the proximal insulated portion of the conductive element (6p). The first structural element features a recess (30) which may reach around the whole circumference of the first structural element. The recess secures the attachment of the casing (31) to the first structural element. The void/lumen (annular channel) (29a) between the proximal insulated portion of the conductive element and the first structural element is sufficient for the proximal insulated portion of the element to slide with respect to the first structural element. The casing comprising 1.sup.st layer (31) and 2.sup.nd layer (32) can be of Parylenen C. Alternatively, 1.sup.st (31) and 2.sup.nd layers (32) can be made of different material. The 2.sup.nd layer (32) may be of a material different from the material of the 1.sup.st layer. Said 2.sup.nd layer (32) may be a layer which exhibits increased friction with respect to the surrounding soft tissue compered to the material of the 1.sup.st layer. Alternatively, or additionally, the outer surface of the 2.sup.nd layer may exhibit a friction inducing surface structure.

[0208] FIG. 5b illustrates a variant sharing many of the design elements of the microelectrode of FIG. 5a with a difference that a second structural component (SC) is situated within the distal compartment (11d). The second structural component stabilizes the distal non-insulated portion (6d) of the element in radial (lateral) direction. Even if the soft tissue surrounding the microelectrode would move extensively displacing the casing extensively with respect to the element the second structural component (SC) stabilizes the radial movement of the distal non-insulated portion (6d) of the element resulting that the perpendicular distance between the distal non-insulated portion 6d of the element and the opening 14 remains similar over time.

[0209] Manufacture of a Microelectrode of the Invention.

[0210] FIG. 6 to 16 show several consecutive steps of one method of manufacturing of a microelectrode probe featuring a first structural component integrated with the casing.

[0211] A metallic filament (conductive element) (18) is fastened at both ends to a frame (19).

[0212] The metallic filament comprises a section (18a) which specifically enables the filament to flex in axial direction (FIG. 6). FIG. 6a shows a frame (19) with a conductive element (18) which does not comprise a section enabling the element to flex in axial direction. In a subsequent step a portion (6p) of the filament is covered with an electrically insulating non-degradable material (15), thereby forming the proximal insulated portion of the conductive element (6p). A distal portion of the conductive element (18) is not covered (6d) thereby providing the prerequisite for forming a distal non-insulated portion of the conductive element. Next (FIG. 8) a distal matrix (20d) is formed radially around the distal portion of the non-insulated conductive element and part of the distal section (21) of the proximal insulated portion of the element. It is important that the matrix also covers part of the proximal insulated portion of the element (21). In FIG. 9 a proximal matrix (20p) is applied radially around part of the proximal insulated portion of the element (6p). An intermediate section (22) remains uncovered by matrix or preferably a thin layer of matrix of biocompatible material is dissolvable or degradable in aqueous body fluids or other composition/substance, such as a composition facilitating the movement of the first structural element with respect to the insulated portion of the conductive element (23) (FIG. 10) is applied to the intermediate section around the element defining a void/lumen (annular channel) (23) between a 1.sup.st layer of electrically insulating non-degradable material (such as parylenen) (24) (FIG. 11). If a matrix or composition/substance is applied around the intermediate section of the proximal insulated portion of the conductive element such composition/substance may also facilitate axial movement of the casing (first structural element) and/or modulate the electric impedance between the proximal and distal compartments. FIG. 11 shows a 1.sup.st layer of electrically insulating non-degradable material (24) applied to the distal matrix (DM), intermediate section, and proximal matrix (PM). In a further step (FIG. 12) the non-insulated conductive element (6d), distal matrix (20d) and 1.sup.st layer (24) are cut radially at a section F-F (FIG. 11) whereby a distal opening (25) is formed which in a subsequent step (FIG. 13) is covered by a distal cap (tip) matrix (26) of a spherical form. FIG. 14 depicts a 2.sup.nd layer of electrically insulating non-degradable material (27) covering the distal cap matrix (26) and 1.sup.st electrically insulating layer of electrically insulating non-degradable material (24). An opening (14) (FIG. 15) is provided through the casing encapsulating the distal chamber at an allocation G (FIG. 14). Furthermore, 1.sup.st and 2.sup.nd electrically insulating layers (24, 27) are removed around a circumferential band of height H forming an annular zone (28, FIG. 15) not covered by electrically insulating non-degradable material. The opening may be accomplished by laser evaporation and optionally followed by laser milling evaporation (FIG. 15).

[0213] The positioning and axial extent of the circumferential band may vary dependent on the types of tissues to be penetrated by the microelectrode probe.

[0214] The opening (or openings) is/are preferably positioned axially with respect to the non-insulated element such that the (perpendicular) distance between the non-insulated element and the opening(s) remain(s) essentially similar when the non-insulated element moves axially. In a final step (FIG. 16) the proto microelectrode is covered by an embedding matrix (28) of biocompatible material dissolvable or degradable in aqueous body fluids. The embedding matrix can be formed by spray coating gelatin in a dry atmosphere. The microelectrodes of FIGS. 15 and 16 are both suitable to be inserted into soft tissue. Hence, FIGS. 15 and 16 present microelectrode probes. FIG. 16 also illustrates a cover (7) attached to the proximal face of the casing, the casing formed by 1.sup.st and 2.sup.nd electrically insulating layer of an electrically insulating non-degradable material. 1.sup.st and 2.sup.nd electrically insulating layer are preferably of Parylene C.

[0215] FIG. 17 to 19 depict the microelectrode probe in various states after introduction into soft tissue (3) such as brain tissue. FIG. 17 presents the microelectrode probe immediately after inserted into brain tissue (3) through the skull bone (1) and tissue (2) intermediate between the skull bone such as dura mater, arachnoid membrane, cerebrospinal fluid, and pia mater (1) and brain tissue (3) (neuronal tissue) and prior to the dissolution of matrices. The two discontinued lines DL illustrate tissue regions which may have different characteristics as to e.g. the tendency for spatial movement (2 and 3).

[0216] FIG. 18 indicates a partial dissolution of the embedding matrix (28).

[0217] FIG. 19 illustrates a state of the microelectrode probe after complete dissolution of the embedding matrix and partial dissolution of distal (DM) and proximal (PM) matrices.

[0218] FIG. 19a is an example of a configuration of a microelectrode after complete dissolution of all matrices showing spatial movement of surrounding soft tissue. The casing (13) which may comprise 1.sup.st and 2.sup.nd electrically insulating layers of electrically insulating non-degradable material has attached (associated) to the surrounding soft tissue at a degree for being able to accommodate to the spatial movements of the soft tissue. The microelectrode also comprises a structural component SC stabilizing the movement of the non-insulated distal portion of the element (6d). The structural component SC is configured such that the distal portion of the element 6d can move in axial direction without much friction, yet, stabilizing the distal proportion sufficiently radially (laterally) that the (perpendicular) distance between distal non-insulated portion of element with respect to the opening 14 remains essentially same. Once the casing has attached to the surrounding tissue the opening of the casing communicates with essentially the same region of the soft tissue over time even when the soft tissue is moving.

[0219] FIG. 20 illustrate an array of four microelectrodes (37a), (37b), (37c), (37d). The microelectrodes are embedded in an array matrix (38).

[0220] FIG. 21 illustrates a cross-section of an array at allocation P showing the array matrix (38), a casing encapsulating a distal compartment (39) and a distal non-insulated portion of the conductive element (40).

[0221] FIG. 22 illustrates a manufacturing step in the manufacturing of a microelectrode with a first structural element (29) of a different material than the casing. The first structural element is positioned around the proximal insulated portion of a conductive element (36) and placed within one first half of a mold (34) of silicone. The second half of the mold properly is positioned with regard to the first half of the mold. Before casting the proximal and distal matrices it is preferred to position the element centrally with respect to the mold.

[0222] FIG. 23 shows a perspective view of first structural component (29) and the central axis as a dashed line.

[0223] FIG. 24 shows a variant of the microelectrode comprising a conductive element (101). A proximal portion of the conductive element (106) is insulated with an electrically insulating non-degradable material (100) while a distal portion of the conductive element is non-insulated (105). A casing (107) of flexible electrically insulating non-degradable material encapsulates the non-insulated portion of the conductive element (105) forming a distal chamber (102). The casing of the distal chamber comprises an opening (103). The inner radial extension of the casing is such that it provides a void/lumen (108) between the casing and the insulated portion of the conductive element (106) for enabling an axial movement of the casing with respect to the conductive element. The numeral (104) visualizes what is meant by the perpendicular distance between the non-insulated portion of the conductive element (105) and the opening (103).

[0224] FIG. 25 presents a first array of microelectrodes attached to one another by micro- or nano-fibers (205). The conductive element (206), first structural components (204), casing (207), distal chambers (202), and opening in the casing of the distal chambers (203) are shown. For reasons of simplicity, the insulation of the conductive elements are not indicated. An array of microelectrodes attached to one another by micro- or nano-fibers preferably having an extension providing a patch. The individual microelectrodes may be arranged essentially parallel in essentially one plane combined forming an array exhibiting a patch-like global extension. This type of array may be applied for monitoring and/or stimulating spinal nervous tissue.

[0225] FIG. 26 shows a variant of a microelectrode comprising an engagement element (307). The casing (308) exhibits a net of micro- or nano-fibers (306) which preferably are adhesively attached to the external surface of the casing. The micro- or nano-fibers increase friction of the casing with respect to the surrounding soft tissue. FIG. 26 also presents a void/lumen (annular channel) (305) between the first structural component (304) and the insulation (300) around the conductive element (301) and surrounding the insulated portion of the proximal conductive element (309). For reasons of clarity the dimensions of the void are exaggerated. The engagement element is configured to reversibly engage with an elongated rigid pin such as a needle (not shown). The pin is further configured to insert the microelectrode into the soft tissue or placing the microelectrode adjacent to soft tissue.