DE19750043A1 - Novel cuff electrode and method for producing it - Google Patents

Abstract

The present invention relates to a configuration which comprises multiple electrodes placed on a flexible substrate and which can be used in the fields of medicine and biology. State-of-the-art electrodes are commonly made of wires introduced into the tissues or comprise metal plates inserted by hand in between silicon layers. These electrodes usually cause wounds in the nerve tissues and finally induce nerve cell death or restrain the positioning precision as well as the number of electrodes. The purpose of this invention is to provide electrode configurations with a large number of electric poles, well-defined electrode surfaces and a precise distance between the different electrodes as well as between the electrodes and the tissues. To this end, the method implies the special use and the perfecting of micro-structure and micro-system techniques on bio-compatible and flexible materials such as polyimide and silicone. This method comprises forming and encapsulating metallic electrodes and inter-connection tracks on bio-compatible materials according to the thin-film techniques. The new Cuff electrode is manufactured by joining two polymer sheets having a high E modulus on an intermediate elastomer layer having a low E modulus so as to obtain the desired final shape.

Description

The invention relates to an arrangement of electrodes according to the preamble in claim 1 for use in the biological and medical field.

The ones known today for stimulating or measuring electrical signals in human beings Body electrodes are either made up of individual wires attached to the tissue be introduced, or from flat, manually embedded between silicone layers Metal plates (selfsizing cuff electrodes, Claude Verrat et al "Selective Control of Muscle Activation with a Multipolar Nerve Cuff Electrode ", IEEE Transaction of Bioamedical Engineering, Vol. 40 No 7, July 93).

The individual wire electrodes placed in the tissue lead to an injury to the Nerve tissue, which leads to severe scarring initially leading to poorer care and ultimately leads to the death of the corresponding nerve cells. This disadvantage is at Use of cuft electrodes, which are embedded in silicon plates and around the nerve laying around, avoided. On the other hand, the manual production of the cuff electrodes limits (manual cutting of the platinum electrodes, manual positioning between silicone Layers) the placement accuracy, the reproducibility of the electrode surfaces and the  Number of electrodes. This makes their use in the medical field strong limited.

A further development of the above manually made cuff electrodes are made by Grill, Creasey, Ksienski, Verrart and Mortimer proposed variant (WO 93/20887). Here are the Electrodes on a film made of polymer material using thin-film technology. Of the The advantage here is that the electrode structures are produced with much higher precision can be as in the manually made variant. So that this electrode is placed around the nerve can be, just like the manually made variant between two Elastomeric platelets (preferably silicone) are embedded, with a platelet in front of the Adhesion of the stack is generated by well-defined stretching a certain tensile stress. After relaxing the stack, it rolls up into a cylindrical roll, whereby the resulting diameter of the roll from the thickness of the platelets, the modulus of elasticity of the used materials, as well as the previously set tension. The above Authors of the Publication WO 93/20887 also propose other methods, all of which result in in the case of the polymer platelets (covering the embedded carrier film), a tensile stress on the inside and / or to generate a compressive stress on the outside. This type of cuff electrode manufacture will also mentioned in WO 96/08290 by Stieglitz and Meyer. Alternatively, Stieglitz and Meyer beat the use of shape memory alloys. The technical Realizability with the help of shape memory alloys, however, seems doubtful.

To our knowledge, a technical implementation of a cuff electrode is still appropriate today the descriptions WO 93/20887 and WO 96/08290 are not carried out. The reason for that It is possible that only materials (PI, PE, PTFE;...) are used for the embedded polymer film a relatively high modulus of elasticity come into question for the outer elastomer platelets Due to the biocompatibility only silicone with its very low modulus of elasticity is in question is coming. It follows that the necessary thickness of the stretched silicone plate can be very large must, and the practical applicability of the entire cuff electrode is questioned.

Furthermore, electrode arrangements that were previously available are not simultaneously one site-specific and nerve-diameter-specific stimulation possible. Since a nerve (cranial nerve, Spinal cord nerve or peripheral nerve) but consists of many thousands of individual nerve fibers,  it must be the goal of every stimulation, as selectively as possible individual nerve fibers of an entire nerve irritate without damaging the cell structure of the nerve. Individual nerve fibers of a nerve differ in their location in the nerve and in their Fiber diameter. So far, it has only been possible to selectively stimulate with regard to the Fiber diameter or fiber localization, but not both at the same time Selection criteria to be considered.

The object of the invention is to make electrode arrangements with a higher number of electrical poles defined electrode areas, precise distance between the electrodes and the tissue to provide simultaneous location and diameter selective stimulation in the µm range to be able to perform. Another requirement of the electrode is that it be designed should be very thin-walled (<100 µm). Such electrode arrangements can for example Stimulation of spinal nerves or the optic nerve can be used.

For this purpose, a polymer carrier on which a conductor track structure has been applied must form a "Cuff" with a diameter corresponding to the nerve size in the range of a few Millimeters up to a few tenths of a millimeter. You must be nervous wrap around without "squeezing" it, but also be firm enough to move relatively to prevent nerves. A peculiarity regarding the requirements for this "cuff" is that the shape of the nerve does not necessarily have to be circular, but that Profile of the nerve cross section should be adapted. A procedure for this is as follows described.

The task is accomplished through a special application and further development of Microstructure techniques and microsystem technology on biocompatible, flexible materials (Polyimide, silicone) solved. Metal electrodes and conductor tracks are made using thin-film technology produced and encapsulated on biocompatible materials. The generation of the novel cuff Electrode is made by connecting two polymer films with high modulus of elasticity via one Intermediate layer consisting of an elastomer with a low modulus of elasticity in the desired Final shape, as described in claim 1.

Advantages of the invention are:

• - Enabling extremely thin-walled electrodes (a wall thickness <100 µm has already been realized!),
• - adaptation of the electrode carrier to tissue shapes that are not cylindrical symmetrical,
• - Good adaptation of the electrode structure to the material properties of suitable biocompatible Materials (polyimide, silicone),
• - Simultaneous location- and parameter-selective stimulation of the nerve with extremely precise placement the electrode surfaces to the nerve tissue,
• - Possibility of manufacturing in large quantities (batch processing) combined with Cost reduction.

Exemplary embodiments of the invention are explained below with reference to a drawing. The Figures of the drawing show:

Fig. 1 is a schematic arrangement of the application of a system with 8 dual-selective scanning electrodes to the nerve roots;

FIG. 2a: executing a dual-selective scanning electrode;

Fig. 2b: Scheme of a 3-polar axial / 6-polar radial electrode. For illustration purposes, carrier film ( 2 ) and electronics ( 4 ) are not shown;

FIG. 3 shows a schematic procedure for preparation of a novel cuff electrode.

Fig. 4: perspective-schematic representation of a novel cuff electrode. The electrode openings or contact openings in the inner passivation layer are not shown. To show the layer structure, the layer thicknesses are greatly exaggerated! A higher number of turns than that shown is also possible.

Example description

The scanner electrode is to be implanted together with control and evaluation electronics as a system ( FIG. 1) in order to establish sensitive and motor-related biotechnical connections (bladder control, standing and walking apparatus) in patients with interrupted stimulation conduction (e.g. cross-sectional violation). An overall system consists of several dual-selective electrodes (FIGS . 2a, 2b), which are each arranged on a bandage of flexible carrier foils ( 2 ), which are wound around the nerves ( 3 ). In this way, in connection with the electronics ( 4 ) arranged decentrally on the carriers, local detection of sensory signals and local stimulation of the tissue can be achieved.

For this purpose, an arrangement of a plurality of electrodes which read out or stimulate independently of one another must be arranged on each carrier ( FIG. 2b, example for 3-polar axial / 6-polar radial arrangement). The 3-polar axial arrangement remains the same for all applications, while the radial arrangement of the electrodes can be multiplied for higher spatial resolutions.

The electrodes are manufactured (for a schematic procedure, see Fig. 3) by applying and further developing thin-film techniques, including organic, biocompatible materials (polyimides, silicone):

As starting carrier sheet (2 a) is a flexible plastic (eg., Polyimide or silicone) is used which is applied as a film for ease of handling on a hard, flat support. A metal conductor pattern structure ( 2 b) is produced on this film via additive or subtractive structure transfer (see, for example, BSM Sze, VLSI Technology McGraw-Hill, 1988). A thin, biocompatible insulating film (a passivation layer, 2 c) is applied over this metal conductor structure. The passivation ( 2 c) of the metallization is carried out, for example, by spinning on liquid silicone, which is structured after the crosslinking reaction, for example with the aid of laser ablation or photolithography and dry etching techniques, around the electrodes ( 5 a) and the contact points ( 5 b) to the electronics ( 4 ) to expose.

To passivate the back of the film, it is detached from the carrier, turned, attached again to a flat carrier and also coated, for example, by spinning on silicone ( 2 d in the illustration before the crosslinking reaction). To form the starting carrier film, a second polyimide film ( 2 f) is applied to the still uncrosslinked silicone of the first film and this "sandwich" is rolled up and fixed in its final form. The back of the second film was also previously passivated, for example by spinning on silicone ( 2 g). After crosslinking of the silicone intermediate layer (2 e), the "cuff" or the novel cuff electrode in the shape is maintained, in which it was fixed during the crosslinking reaction. It is therefore also possible to produce non-cylindrical cross sections. On the other hand, the "soft" elastomer between the "hard" polyimide films also enables the electrode to be springily unwound in order to apply it to the nerve. Left alone, the electrode snaps back into its original shape.

After connecting the electronics ( 4 ) and the carrier film composite ( 2 ), for example using flip-chip technology, the entire subsystem, with the exception of the electrodes ( 5 a), is encapsulated with liquid silicone ( 10 ). The individual subsystems are connected by covered wires ( 9 ).

After implantation of the entire system, the stimulation pattern applied via the scanner electrodes is adapted to the individual situation of the patient via a neural network integrated in the electronics ( 4 , 11 ). Newly developed multitrapezoidal current impulses with the setting parameters stimulus form, stimulus distance, stimulus frequency, stimulus current and stimulus rhythm (on-off phases) are used for stimulation.

Claims (10)

1. Multiple arrangement of electrodes on a flexible support for use in the biological-medical field, characterized in that two thin polymer films with a high modulus of elasticity are connected via a thin intermediate layer made of an elastomer with a low modulus of elasticity to form the support and this film composite Cuff forms, the shape of which can be adapted to any (even non-circular) nerve cross-section. 2. Electrode arrangement according to claim 1, characterized in that the electrodes on the flexible support by thin or Thick film techniques are applied and structured. 3. electrode arrangement according to claim 1 and 2, characterized in that several are applied radially and axially around the nerve to be stimulated Electrodes are arranged on a common carrier film (multipolar arrangement). 4. electrode arrangement according to claim 1, characterized in that the electrodes are structured by a spun and subtractive structure Polyimide or silicone layer are passivated. 5. electrode arrangement according to claim 1 and 4, characterized in that the silicon passivation by means of photolithography and Dry etching or laser ablation is structured. 6. electrode arrangement according to claim 1, characterized in that the encapsulation of the electrode carrier by spun silicone is made.   7. electrode arrangement according to claim 1, characterized in that the electrode mechanically and electrically using hybrid techniques the control and evaluation electronics are connected. 8. electrode arrangement according to claim 1, characterized in that several electrodes are electronically connected to form a system and can be controlled synchronized. 9. electrode arrangement according to claim 1, characterized by stimulation of the electrodes with multitrapezoid signals. 10. Electrode arrangement according to claim 1, characterized in that the stimulation signals can be adapted postoperatively via neural networks are.