WO2024120719A1

WO2024120719A1 - Implantable electrode for an implantable medical device

Info

Publication number: WO2024120719A1
Application number: PCT/EP2023/081005
Authority: WO
Inventors: Eckardt Bihler; Marc Robert Hauer
Original assignee: Dyconex Ag
Priority date: 2022-12-06
Filing date: 2023-11-07
Publication date: 2024-06-13

Abstract

The present invention relates to an implantable electrode (1) for an implantable medical device, the implantable electrode (1) having a substrate (2) comprising a substrate material (20); an electrode pole (3); and a connecting line (9) extending within the substrate (2), wherein the electrode pole (3) comprises an electrode pole surface (30) that is arranged on a surface of the substrate (2) and a contact line (33) electrically connecting the electrode pole surface (30) with the connecting line (9). According to an aspect of the invention, in a cross section of the implantable electrode (1), the electrode pole surface (30), a first section (31) of the contact line (33), a second section (32) of the contact line (33), and a section of the connecting line (9) at least partially surround a space (10) that is filled with the substrate material (20).

Description

Implantable electrode for an implantable medical device

The present invention relates to an implantable electrode for an implantable medical device according to the preamble of claim 1, to an implantable medical device comprising such an electrode according to the preamble of claim 13, and to two methods for manufacturing an implantable electrode according to the preambles of claims 14 and 15.

According to prior art techniques, implantable electrodes are formed on a polymeric substrate by depositing thin metal structures. However, these metal structures often show an insufficient long-term stability in an aqueous environment like in a patient’s body. To enhance the adhesion between such thin metal structures and the polymeric substrate as well as limit the risk of a pre-mature separation between the metallic structures and the polymeric substrate, prior art teaches to provide a connection line that is vertically arranged to the surface of the electrode and that is embedded in the polymeric substrate. While this arrangement enhances the stability of the connection between the metallic parts of the electrode and the substrate, the long-term stability has not yet reached the desired level.

It is an object of the present invention to provide an implantable electrode comprising metal structures that show a higher stability and a lower risk of delamination and separation from a substrate on which the metallic structures are applied.

This object is achieved with an implantable electrode having the claim elements of claim 1. Such an implantable electrode is intended to be used together with an implantable medical device. The implantable electrode has a substrate that is made from a subset material. Furthermore, it has an electrode pole that is partially embedded into the substrate. The electrode furthermore comprises a connecting line that extends within the substrate. The electrode pole comprises an electrode pole surface that is arranged on the surface of the substrate. The electrode pole further comprises a contact line that electrically connects the electrode pole surface with the connecting line.

According to an aspect of the present invention, the electrode has a special design in a cross section of the electrode that enhances the durability of the electrode and guarantees for a high long-term stability of the electrode. In the cross section of the electrode, the electrode pole surface, a first section of the contact line, a second section of the contact line, and a section of the connecting line at least partially surround a space that is filled with the substrate material. In contrast to prior art solutions that make use of a vertical connecting line (and optionally of an anchor element provided at the end of the connecting line) embedded into the substrate material, the presently claimed implantable electrode provides with the (almost) enclosed space formed by metallic parts of the electrode around and within the substrate material a structure that enables a significantly higher stability of the electrode.

Due to an undercut of the structure surrounding at least partially the space filled with the substrate material, it is mechanically impossible for the electrode pole surface to be separated from the surface of the substrate. The inventors came to the conclusion that the adhesion of the metal surfaces on the substrate are determined by the strength of the atomic bonds within the metal structures and not by the bonds between the metal structures and the surface of the (polymeric) substrate. Thus, the present invention aims in increasing the overall strength of the atomic bonds within the metal structures of the electrode. This is done by forming a cagelike arrangement of the electrode pole surface, the first section of the contact line, the second section of the contact line, and the section of the connecting line. This cage-like structure serves for a significantly higher adherence of these metallic parts on and within the substrate than in case of prior art arrangements. This adherence stably persists after implantation of the implantable electrode in a patient’s body over the whole intended lifetime of an implantable medical device being equipped with the implantable electrode. This could be proven by the inventors by tensile tests performed after having incubated the implantable electrode in an aqueous solution simulating a body fluid.

In an embodiment, the first section of the contact line and the second section of the contact line extend, in the cross section, from the electrode pole surface to the connecting line without interruption. Thus, in a cross-sectional view, there are at least two contact line sections that serve for a good adherence of the electrode pole surface to the substrate. In contrast, prior art only teaches to use a single connecting line (if at all) to electrically connect and to stabilize an electrode pole surface.

In an embodiment, the electrode pole surface, the first section of the contact line, the second section of the contact line, and the section of the connecting line fully surround, in the cross section, the space that is filled with the substrate material. By fully surrounding the space, a cage around the space is formed, wherein the cage is (fully) filled with the substrate material. Thus, the first section of the contact line, the second section of the contact line, and the section of the connecting line are fully embedded within the substrate material, wherein the electrode pole surface is applied on top of the substrate and thus is able to get into electrical contact with surrounding environment of the implantable electrode. By fully surrounding the substrate-material filled space, the retention and stabilizing forces that act upon the electrode pole surface are particularly high so that an adherence of the electrode pole surface to the substrate is particularly high and durable.

In an embodiment, the first section of the contact line and the second section of the contact line extend angularly to each other. E.g., a distance between the first section of the contact line and the second section of the contact line is, in the cross section, smaller or bigger in a region of the first section of the contact line and the second section of the contact line that is adjacent to the electrode pole surface than a distance between the first section of the contact line and the second section of the contact line in a region of the first section of the contact line and the second section of the contact line that is more distant to the electrode pole surface.

In an embodiment, the first section of the contact line and the second section of the contact line extend, in the cross section, parallel to each other. If the electrode pole surface and the section of the connecting line also extend parallel to each other, a rectangular or quadratic structure is formed by the electrode pole surface, the first section of the contact line, the second section of the contact line and the section of the connecting line in the cross section of the electrode. An interior of this rectangular or quadratic structure then corresponds to the space that is filled with a substrate material.

In an embodiment, the section of the connecting line has, in the cross section, the same width as the electrode pole surface. Then, the connecting line does not protrude from the first section of the contact line nor from the second section of the contact line into the substrate material in the cross section of the electrode.

In an embodiment, the electrode pole surface, the first section of the contact line, the second section of the contact line, and a section of the connecting line are, in the cross section, flush with each other. Thus, in this embodiment, none of the previously mentioned metallic elements protrudes from another of these metallic elements. Then, a partially open or fully closed structure like a rectangle or square is formed by the electrode pole surface, the first section of the contact line, the second section of the contact line, and the section of the connecting line in the cross section of the implantable electrode. In this context, the rectangle or square has flush outer surfaces. Such a design significantly reduces the risk of damaging the metallic structures of the electrode pole surface, the first section of the contact line, the second section of the contact line, and the section of the connecting line that could otherwise occur in case of individual overhanging sections of any of these elements.

In an embodiment, the electrode pole comprises a supplementary electrode pole having a supplementary electrode pole surface that surrounds the (principal) electrode pole surface. In this context, the supplementary electrode pole surface is electrically connected to the connection line by a supplementary contact line. By such a supplementary electrode pole, the effective electrode pole surface can be increased, thus facilitating the transfer of electric pulses between the implantable electrode and surrounding body tissue or body fluid.

In an embodiment, the supplementary electrode pole and the (principal) electrode pole are concentrically arranged to each other.

In an embodiment, the implantable electrode comprises a groove in the electrode substrate between the electrode pole and the supplementary electrode pole. This groove serves for a non-material filled space between the (principal) electrode pole and the supplementary electrode pole. In an embodiment, the groove makes possible an electrical contact between the connecting line and a body tissue or body fluid surrounding the implantable electrode in its implanted state. Then, not only the (principal) electrode pole surface and the supplementary electrode pole surface can effect an electrical pulse transfer between the implantable electrode and a patient’s body, but also the surface of the connecting line and a surface of the first section of the contact line and a surface of the second section of the contact line. This significantly enhances the effective electrode pole surface, This may be helpful in various applications of the implantable electrode.

In an embodiment, the groove between the (principal) electrode pole and the supplementary electrode pole is filled with the substrate material.

In an embodiment, the groove between the (principal) electrode pole and the supplementary electrode pole is filled with a material distinct from the substrate material. In such a case, the groove is no longer present as groove, but it differentiates itself from the remaining part of the substrate due to the different material by which it is filled. In doing so, the electric properties of the electrode pole can be fine-tuned according to the respective needs.

In an embodiment, the groove has a width, in the cross section, lying in a range of from 0.002 mm to 0.1 mm, in particular from 0.005 mm to 0.05 mm, in particular from 0.01 mm to 0.04 mm, in particular from 0.02 mm to 0.03 mm.

In an embodiment, the substrate material is preferrable sheets made from a liquid crystal polymer (LCP) or a polyimide., however also other polymer substrate materials may be used. In an embodiment, the substrate material is formed as a sheet. A. The above stated polymer materials, particularly formed as a sheet, may be used for a multilayer flexible substrate and may be structured by a photolithographic printing technique. It allows rather a two- dimensional result than a three-dimensional result due to very small thicknesses that can be achieved by using such sheet polymers. Furthermore, the above stated polymer materials, particularly formed as a sheet, allows a very good integration of individual components into the substrate of the implantable electrode and guarantees an easy manufacturing in a very robust, reliable and reproducible manner. Particularly, a liquid crystal polymer is biocompatible, does not degrade in the body environment, and it has very low moisture absorption and moisture penetration properties, which make LCP a preferrable choice for implanted electrodes

In an embodiment, the substrate is entirely made of the substrate material. In another embodiment, the substrate comprises a first substrate material and a second substrate material that is used for applying a covering layer onto the first substrate material and/or onto metallic structures such as the contact line and/or the connecting line or sections thereof.

In an embodiment, the substrate has a thickness lying in a range of from 0.01 mm to 0.2 mm, in particular from 0.05 mm to 0.1 mm, in particular from 0.07 mm to 0.09 mm.

In an embodiment, the electrode pole comprises a layer of gold having a thickness lying in a range of from 0.001 mm to 0.05 mm, in particular from 0.005 mm to 0.01 mm, in particular from 0.01 mm to 0.03 mm.

In an embodiment, the electrode pole comprises a seed layer comprising or entirely consisting of palladium, wherein a layer of gold is applied onto the seed layer. In an embodiment, not only the electrode pole, but also the other metallic structures (such as the contact line and/or the connecting line) comprise layer of gold and/or a seed layer made of or comprising palladium. In an embodiment, all metallic structures have the same chemical and/or physical composition. This embodiment facilitates the realization of the metallic structures of the implantable electrode.

In an aspect, the present invention relates to an implantable medical device that comprises an implantable electrode according to the preceding explanations. Due to the high durability and long-term stability of this implantable electrode, the lifetime of the implantable medical device can be extended or, at least, is not limited due to limited lifetime of a connected electrode. In an embodiment, the implantable medical device is an implantable neurostimulator, an implantable pulse generator (IPG), an implantable cardioverter-defibrillator (ICD), a device for cardiac resynchronization therapy (CRT), or an implantable cardiac monitor. An appropriate cardiac monitor is a loop recorder.

In an aspect, the present invention relates to a method for manufacturing an implantable electrode according to the preceding explanations. This method comprises the steps explained in the following.

In a first method step, a substrate layer made from substrate material is provided.

Afterwards, a working groove is formed into the substrate layer by removing a part of the substrate material around an area in which an electrode pole is to be formed. The working groove can be formed, e.g., by laser ablation. The working groove is not self-contained. Rather, a connecting bar of substrate material remains present between the area in which the electrode pole is to be formed and the substrate material outside this area. Typically, not only a single connecting bar remains present, but rather two or more connecting bars. In an embodiment, the connecting bars are equally distributed around the circumference of the area in which the electrode pole is to be formed.

Afterwards, the area in which the electrode pole is to be formed is metallized on the front side of the substrate. This results in formation of the electrode pole surface.

Prior to, concomitantly with, or after this metallizing step, a section of the bottom side of the substrate is metallized. This results in formation of a connecting line.

Prior to, concomitantly with, or subsequent to one or both of the previously mentioned metallizing steps, inner side walls of the working groove are metallized. This results in formation of a contact line. In this context, the contact line electrically connects the electrode pole with the connection line. Metallizing can be done, e.g., galvanically, i.e., by depositing a metal like gold in a galvanic process onto the substrate.

After the metallizing steps, a covering layer is applied onto the bottom side of the substrate layer and into the working groove. Expressed in other words, the connecting line is covered by the covering layer, and the working groove is filled by the covering layer. The covering layer may be made from the substrate material or, alternatively, from a material different from the substrate material. After having applied the covering layer, the contact line and the connecting line are embedded in the substrate. Thereby, the connecting line, the contact line and the electrode pole surface are arranged such that the electrode pole surface, a first section of the contact line, a second section of the contact line, and a section of the connecting line at least partially surround, in a cross section of the electrode, a space that is filled with the substrate material. Thus, inside the arrangement of the structure formed by the electrode pole surface, the contact line and the connecting line, the substrate material is present, wherein outside the contact line and the connecting line, the covering layer is applied. This arrangement serves for a very stable connection between the electrode pole surface and the substrate material onto which the electrode pole surface is metallized.

In an aspect, the present invention relates to an alternative manufacturing method for producing an implantable electrode according to the preceding explanations. According to this alternative manufacturing method, a substrate layer is provided in a first step. Afterwards, a section of a front side of the substrate layer is metallized so as to form a connecting line.

Afterwards, a covering layer is applied onto the front side of the substrate layer. This covering layer covers the connecting line.

Subsequently, a groove is formed into the covering layer by removing part of the covering layer around an area in which an electrode pole is to be formed. In this context, the groove extends up to the connecting line. Afterwards, the area in which the electrode pole is to be formed is metallized on a front side of the covering layer. This results in formation of an electrode pole surface.

Prior to, concomitantly with or subsequent to the previously explained metallizing step, at least an inner side wall of the groove is metallized so as to form a contact line. The contact line electrically connects the electrode pole surface with the connecting line. The resulting structure of metallized elements of the implantable electrode is designed such that the electrode pole surface, a first section of the contact line, a second section of the contact line, and a section of the connecting line at least partially surround, in a cross section of the electrode, a space that is filled with the covering layer.

In an embodiment, not only the inner side walls of the groove are metallized, but also the outer side walls of the grove. Then, a supplementary electrode pole is formed. In this context, the supplementary electrode pole is electrically connected to the connecting line by a supplementary contact line. In addition, the supplementary electrode pole surrounds the (principal) electrode pole and thus increases the effective electrode pole surface.

All embodiments of the implantable electrode can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the implantable medical device, and to the manufacturing methods. Likewise, all embodiments of the implantable medical device can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the implantable electrode and to the manufacturing methods. Finally, all embodiments of the manufacturing methods can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the implantable electrode, to the implantable medical device, and to the respective other manufacturing method.

Further details of aspects of the present invention will be explained in the following making reference to exemplary embodiments and accompanying Figures. In the Figures:

Figure 1 A shows a top view onto an implantable electrode according to prior art; Figure IB shows a cross-sectional view through the prior art electrode of Figure 1 A;

Figure 2A shows a top view onto an implantable electrode according to a first embodiment;

Figure 2B shows a first cross-sectional view through the implantable electrode of Figure 2A along the line marked with B-B in Figure 2A;

Figure 2C shows a second cross-sectional view through the implantable electrode of Figure 2A along the line marked with C-C in Figure 2A;

Figure 3A shows a top view onto an implantable electrode according to a second embodiment;

Figure 3B shows a first cross-sectional view through the implantable electrode of Figure 3 A along the line marked with B-B in Figure 3 A;

Figure 3C shows a second cross-sectional view through the implantable electrode of Figure 3 A along the line marked with C-C in Figure 3 A;

Figure 4A shows a top view onto an implantable electrode according to a third embodiment;

Figure 4B shows a first cross-sectional view through the implantable electrode of Figure 4A along the line marked with B-B in Figure 4A;

Figure 4C shows a view onto the bottom side of the electrode of Figure 4A;

Figure 4D shows a second cross-sectional view through the implantable electrode of Figure 4A along the line D-D of Figure 4A;

Figure 5A shows the same electrode as Figure 4A in a top view; Figure 5B shows the electrode of Figure 5 A, wherein an electrode pole and the substrate have been folded onto each other;

Figure 5C shows a cross-sectional view through the electrode of Figure 5 A along the line C-C in Figure 5A;

Figure 5D shows a cross-sectional view through the electrode of Figure 5B along the line D-D in Figure 5B;

Figure 6A shows a top view onto an implantable electrode according to a fourth embodiment;

Figure 6B shows a first cross-sectional view through the implantable electrode of Figure 6A along the line marked with B-B in Figure 6A;

Figure 6C shows a second cross-sectional view through the implantable electrode of Figure 6A along the line marked with C-C in Figure 6A;

Figure 7A shows a top view onto an implantable electrode according to a fifth embodiment;

Figure 7B shows a first cross-sectional view through the implantable electrode of Figure 7A along the line marked with B-B in Figure 7A;

Figure 7C shows a second cross-sectional view through the implantable electrode of Figure 7A along the line marked with C-C in Figure 7A;

Figure 1A shows a top view onto an implantable electrode 1 according to prior art. This implantable electrode 1 comprises a substrate 2 and an electrode pole 3, the surface of which is applied on top of the substrate 2. Figure IB shows a cross-sectional view through the implantable electrode to 1 of Figure 1 A along the line B-B in Figure 1 A. In this and in all following Figures, similar elements will be denoted with the same numeral reference.

In the cross-sectional view of Figure IB, it can be seen that the electrode pole 3 is connected via a contact line 4 with a connecting line 5. The connecting line 5 is applied onto a bottom side of the substrate 2. After having applied the connecting line 5 onto the bottom side of the substrate 2, the bottom side of the substrate 2 is covered with a covering layer 6 that embeds the connecting line 5.

In the cross-sectional view of Figure IB, the electrode 3 forms together with the contact line 4 and the connecting line 5 a double-T structure that helps in reducing the risk of a separation of the electrode pole 3 from the substrate 2.

However, the adherence of the electrode 3 to the substrate 2 can be significantly increased with embodiments of an implantable electrode that will be explained in the following.

Figure 2A shows a top view onto an embodiment of an implantable electrode 1 that comprises a substrate 2 and an electrode pole surface 30. The electrode pole surface 30 is almost fully surrounded by a working groove 7 that is already filled with a covering layer that may be made from a substrate material identical to or different from the substrate material used to build up a substrate layer of the substrate 2. The material of the covering layer is filled into the working groove 7, however, only after having deposited the electrode pole 3 (confer Figure 2B), the electrode pole surface 30 forms part of.

The working groove 7 is formed such that it is not self-contained, but rather allows a connecting bar 8 to establish a permanent connection between an area under the electrode pole surface 30 and the remainder of the substrate 2.

Figure 2B shows a first cross-sectional view through the substrate 1 of Figure 2A along the line B-B in Figure 2A. In this cross-sectional view, it can well be seen that the electrode pole surface 30, a first section 31 of a contact line 33, and a second section 32 of the contact line 33 form together the electrode pole 3. Due to the working groove 7, it is possible to metallize the electrode pole surface 30 as well as the contact line 33 in the same metallizing step around a portion of substrate material 20 that belongs to the substrate layer 21 of the substrate 2 (and is connected to the remainder of the substrate layer 21 via the connecting bar 8 (cf. Figure 2A)).

Upon manufacturing the implantable electrode 1, also a connecting line 9 is metallized onto a bottom side of the substrate layer 21. Once both the electrode pole 3 and the connecting line 9 have been deposited onto a bottom side of the substrate layer 21 in the region of the electrode pole 3, a covering layer 22 is applied onto the bottom side of the substrate layer 21. The substrate layer 21 and the covering layer 22 from together the substrate 2. The covering layer 22 is also filled into the working groove 7 and fills in the working groove 7.

In the resulting structure depicted in Figure 2B, the electrode pole surface 30, the first section 31 of the contact line 33, the second section 32 of the contact line 33 and a section of the connecting line 9 fully surround a space 10 that is filled with a substrate material 20 forming part of the substrate layer 21 and thus of the substrate 2.

Generally, the space 10 need not to be fully enclosed as in the embodiment shown in Figure 2B. Rather, it would be possible that the connecting line 9 has a small interruption by which a direct contact between the substrate material 20 in the space 10 and the covering layer 22 would be established.

Figure 2C shows a second cross-sectional view through the implantable electrode 1 along the line C-C of Figure 2A. Due to the connecting bar 8, the space 10 is not fully enclosed by the electrode pole surface 30, the contact line 33, and the connecting line 9 in this cross- sectional view. Rather, the backside of the space 10 remains open so that there is a direct material connection between the substrate material 20 within the space 10 and the substrate material 20 of the remainder of the substrate layer 21 of the substrate 2.

Figures 3A to 3C show a similar embodiment of an implantable electrode 1, wherein Figure 3A shows a top view, Figure 3B shows a first cross-sectional view along the line B-B of Figure 3A, and Figure 3C shows a second cross-sectional view along the line C-C of Figure 3 A. In the following, only the differences to the embodiment shown in Figures 2A to 2C will be discussed.

In contrast to the embodiment shown in Figures 2A to 2C, the implantable electrode 1 shown in Figures 3A to 3C comprises a second connecting bar 11 in addition to the first connecting bar 8 that serves for a direct material connection between the substrate material 20 located within the space 10 and the remainder of the substrate layer 21 of the substrate 2. By providing not only the first connecting bar 8, but also the second connecting bar 11, a higher stability of the substrate material 20 located within the space 10 can be achieved during manufacturing of the implantable electrode 1. This facilitates the production process and allows an accurate metal deposition of the electrode pole 3 and the connecting line 9.

In the second cross-sectional view of Figure 3C, the second connecting bar 11 is visible instead of the working groove 7 as in case of the embodiment shown in Figure 2C.

In the implantable electrodes 1 shown in Figures 2A to 3C, the connecting line 9 cannot be used for contacting other electrode poles of the same implantable electrode 1. This may be connected to certain disadvantages in application cases in which the whole width of the substrate 2 shall be covered by electrode poles. The embodiment shown in Figures 4A to 5D, however, overcomes this potential disadvantage.

Figure 4A shows a top view onto an implantable electrode 1 in which the electrode pole 3 is cut out of the substrate 2 together with the already filled out working groove 7 over the whole height of the implantable electrode 1. This can be better seen in the first cross-sectional view of Figure 4B which is taken along the line B-B of Figure 4A. The cutout portion comprises the electrode pole surface 30, the first section 31 of the contact line 33, the second section 32 of the contact line 33, the connecting line 9 as well as the covering layer 22 that has been filled into the working groove 7 during the manufacturing process. In addition, the cutout comprises the substrate material 20 being present within the space 10 Figure 4C shows a botom view onto the implantable electrode 1 of Figure 4A, wherein the covering layer 22 is illustrated in a partially transparent form. In doing so, a first supplementary connecting line 91 and a second supplementary collecting line 92 can be seen that extend in parallel to each other, but perpendicular to the connecting line 9. The connecting line 9 is electrically connected to the first supplementary connecting line 91.

Figure 4D shows a second cross-sectional view through the implantable electrode 1 of Figure 4A along the line D-D of Figure 4 A. The second cross-sectional view does not significantly deviate from the second cross-sectional view of the implantable electrode 1 shown in Figure 2C. Since the electrode pole 3 has already been cut from the surrounding material, only a smaller amount of covering layer 22 is present on the outside of the contact line 33. Furthermore, the second supplementary connecting line 92 can be seen in addition to the first supplementary connecting line 91 in the cross-sectional view of Figure 4D. In this context, the first supplementary connecting line 91 stands in electrical contact with the connecting line 9 so that both connecting lines appear to be a single element in the cross- sectional view of Figure 4D.

Figures 5A and 5B show how the electrode pole 3 of the implantable electrode 1 already shown in Figure 4A can be folded onto the substrate 2. For this purpose, the substrate 2 is flapped around line F in the direction of the arrow of Figure 5 A. The resulting situation is shown in Figure 5B. In this context, the substrate 2 is visible from its top side in Figure 5A, wherein it is visible from its bottom side in Figure 5B. Such a folding process cannot be done only with a single electrode pole 3, but with a plurality of electrode poles 3 that extend along the line F. The electrode pole 3 is then - together with the already filled working groove 7 - fixed on the substrate 2 by, e.g., hotmelt.

The folding process is also illustrated in Figures 5C and 5D, wherein Figure 5C shows a cross-sectional view along line C-C of Figure 5A (i.e., prior to the folding process), wherein Figure 5D shows a cross-sectional view along line D-D of Figure 5B, after the folding process has been accomplished. In the depiction of Figure 5C, the substrate 2 with its substrate layer 21 and its covering layer 22 is folded in the direction shown by the arrow around line F. The covering layer 22 is then melted to itself, so that the structure shown in Figure 5D results. This is a very space-saving arrangement of the electrode 3 on the substrate 2 so that a plurality of electrode poles can be positioned next to each other. This is particularly helpful in applications that require a high density of electrode poles, e.g., implantable electrodes for neural stimulation.

Another possibility of increasing the wiring density is the use of a multilayer substrate. An according implantable electrode 1 is shown in Figure 6A. This electrode comprises a substrate 2, an electrode pole 3, a metallized groove 12, and a supplementary electrode 13. This implantable electrode 1 is shown in Figures 6B in a first cross-sectional view along the line B-B of Figure 6A, and in Figure 6C in a second cross-sectional view along the line C-C of Figure 6 A.

To manufacture this implantable electrode 1, the substrate layer 21 is metallized on its top side with the connecting line 9 and on its bottom side with a first supplementary connecting line 91. Afterwards, two covering layers 22 are applied onto the substrate layer 21, namely one covering layer 22 on the top side of the substrate layer 21, and the other on the bottom side thereof. Afterwards, the groove 12 is introduced into the top covering layer 21. Then, the inner and outer sidewalls as well as the bottom of the groove 12 are metallized. In doing so, a contact line 33 comprising a first section 31 and a second section 32 is formed. Furthermore, the supplementary electrode pole 13 is formed on the outer sidewall of the groove 12. The supplementary electrode pole 13 comprises a supplementary electrode pole surface 130 and a supplementary contact line 133. The principal electrode pole 3 and the supplementary electrode pole 13 are electrically connected with each other by the connecting line 9. The first supplementary connecting line 91 can be used for connecting other electrode poles that can be introduced onto the bottom side of the substrate to in the same way as explained for the electrode pole 3 and the supplementary electrode pole 13.

Figure 6C illustrates that the implantable electrode 1 does not only comprise the first supplementary connecting line 91, but also a second supplementary connecting line 92 that both extend along the substrate 2. Figure 7A shows another embodiment of an implantable electrode 1 that is very similar to the embodiment shown in Figure 6A. The only difference here is that only the inner sidewall and the bottom of the groove 12 are metallized, but not the outer sidewall of the groove 12. Therefore, no supplementary electrode pole is formed. However, due to the metallization of the bottom of the groove 12, the effective surface of the electrode pole 3 is also increased.

Figure 7B shows a first cross-sectional view through the implantable electrode 1 of Figure 7A along the line B-B of Figure 7A.

Figure 7C shows a second cross-sectional view through the implantable electrode 1 of Figure 7A along the line C-C. For further explanations of these views, reference is made to the above explanations given with respect to Figures 6B and 6C.

Claims

1. Implantable electrode (1) for an implantable medical device, the implantable electrode (1) having a substrate (2) comprising a substrate material (20), an electrode pole (3), and a connecting line (9) extending within the substrate (2), wherein the electrode pole (3) comprises an electrode pole surface (30) that is arranged on a surface of the substrate

(2) and a contact line (33) electrically connecting the electrode pole surface (30) with the connecting line (9), characterized in that, in a cross section of the implantable electrode (1), the electrode pole surface (30), a first section (31) of the contact line (33), a second section (32) of the contact line (33), and a section of the connecting line (9) at least partially surround a space (10) that is filled with the substrate material (20).

2. Implantable electrode according to claim 1, characterized in that, in the cross section, the first section (31) of the contact line (33) and the second section (32) of the contact line (33) extend from the electrode pole surface (30) to the connecting line (9) without interruption.

3. Implantable electrode according to claim 1 or 2, characterized in that the electrode pole surface (30), the first section (31) of the contact line (33), the second section (32) of the contact line (33), and the section of the connecting line (9) fully surround the space (10) that is filled with the substrate material (20).

4. Implantable electrode according to any of the preceding claims, characterized in that the first section (31) of the contact line (33) and the second section (32) of the contact line (33) extend, in the cross section, parallel to each other.

5. Implantable electrode according to any of the preceding claims, characterized in that the section of the connecting line (9) has, in the cross section, the same width as the electrode pole surface (30).

6. Implantable electrode according to any of the preceding claims, characterized in that the electrode pole surface (30), the first section (31) of the contact line (33), the second section (32) of the contact line (33), and the section of the connecting line (9) are, in the cross section, flush with each other.

7. Implantable electrode according to any of the preceding claims, characterized in that the electrode pole (3) comprises a supplementary electrode pole (13) having a supplementary electrode pole surface (130) surrounding the electrode pole surface (30), wherein the supplementary electrode pole surface (130) is electrically connected to the connection line (9) by a supplementary contact line (133).

8. Implantable electrode according to claim 7, characterized in that the implantable electrode (1) comprises a groove (12) in the substrate (2) between the electrode pole (3) and the supplementary electrode pole (13).

9. Implantable electrode according to claim 8, characterized in that the groove (12) has a width, in the cross section, lying in a range of from 0.002 mm to 0.1 mm.

10. Implantable electrode according to any of the preceding claims, characterized in that the substrate material (20) is a liquid crystal polymer.

11. Implantable electrode according to any of the preceding claims, characterized in that the substrate (2) has a thickness lying in a range of from 0.01 mm to 0.2 mm.

12. Implantable electrode according to any of the preceding claims, characterized in that the electrode pole (3) comprises a layer of gold having a thickness lying in a range of from 0.001 mm to 0.05 mm. Implantable medical device, comprising an implantable electrode (1) according to any of the preceding claims. Method for manufacturing an implantable electrode (1) according to any of claims 1 to 13, comprising the following steps: a) providing a substrate layer (21) comprising a substrate material (20); b) forming a working groove (7) into the substrate layer (21) by removing a part of the substrate material (20) around an area in which an electrode pole (3) is to be formed, wherein the working groove (7) is not self-contained so that a connecting bar (8, 11) of substrate material (20) remains present between the area in which the electrode pole (3) is to be formed and the substrate material (20) outside this area; c) metallizing the area in which the electrode pole (3) is to be formed on a front side of the substrate layer (21) so as to form an electrode pole surface (30); d) metallizing a section of a bottom side of the substrate layer (21) so as to form a connecting line (9); e) metallizing inner sidewalls of the working groove (7) so as to form a contact line (33), wherein the contact line (33) electrically connects the electrode pole surface (30) with the connecting line (9), wherein, in a cross section of the implantable electrode (1), the electrode pole surface (30), a first section (31) of the contact line (33), a second section (32) of the contact line (33), and a section of the connecting line (9) at least partially surround a space (10) that is filled with the substrate material (20); and f) applying a covering layer (22) onto the bottom side of the substrate layer (21) and into the working groove (7). Method for manufacturing an implantable electrode (1) according to any of claims 1 to 13, comprising the following steps: a) providing a substrate layer (21); b) metallizing a section of a front side of the substrate layer (21) so as to form a connecting line (9); c) applying a covering layer (22) comprising substrate material (20) onto the front side of the substrate layer (21) and onto the connecting line (9); d) forming a groove (12) into the covering layer (22) by removing part of the covering layer (22) around an area in which an electrode pole (3) is to be formed, wherein the groove (12) extends up to the connecting line (9); e) metallizing the area in which the electrode pole (3) is to be formed on a front side of the covering layer (22) so as to form an electrode pole surface (30); f) metallizing at least inner sidewalls of the groove (12) so as to form a contact line (33), wherein the contact line (33) electrically connects the electrode pole surface (30) with the connecting line (9), wherein, in a cross section of the electrode, the electrode pole surface (30), a first section (31) of the contact line (33), a second section (32) of the contact line (33), and a section of the connecting line (9) at least partially surround a space (10) that is filled with the substrate material (20).