Flexible electrode

An electrode array has a flexible body supporting a plurality of electrodes. Each electrode comprises an exposed connector pad at the upper end of the body, an exposed recording/stimulating pad at the lower end of the body, and a conductor located within the body and electrically connecting the connector pad and the recording/stimulating pad. In one embodiment the electrode array has an elongated recording/stimulating portion coiled or folded to distribute the exposed recording/stimulating pads in three dimensions. An implantation method employs an introducer with a helical portion to which an end of the flexible electrode is attached. The helical portion straightens to pass through a small-diameter cannula and then resumes its helical configuration to place the recording/stimulating portion of the attached electrode in a helix within the patient's tissues.

TECHNICAL FIELD

This invention relates generally to electrodes for use within the body of a patient and to systems of manufacturing and of implanting such electrodes. More specifically, the invention relates to a flexible electrode that can create a distribution of electrode sites within the interior bulk of a tissue using only one penetration along a single electrode track.

BACKGROUND OF THE INVENTION

When used in medical applications, an electrode is an electrically conductive structure that either electrically stimulates or records the electrical activity of surrounding tissue within the body of a patient. Examples of medical applications for electrodes include deep brain stimulation and brain mapping. Deep brain stimulation electrodes have applications in the treatment of Parkinson's, epilepsy, chronic pain, depression, muscle spasticity, schizophrenia, anxiety, coma, addition, migraine, and Alzheimer's, among others.

Conventional medical electrodes present a number of disadvantages. First, known medical electrode arrays cannot be inserted into tissue without causing trauma to the tissue, a characteristic that is especially disadvantageous in the case of deep brain stimulation and brain mapping electrodes. Consequently, known electrode arrays can only be placed on the surface of the brain, making it impossible to stimulate or detect electrical activity below the surface of the brain without causing trauma to delicate brain tissue.

Second, known medical electrodes are typically denser than the tissue into which they are positioned. Thus any sudden acceleration or deceleration can cause movement of the electrode relative to the tissue, resulting in shearing or abrading of the surrounding tissue.

Third, known medical electrodes are typically less compliant than the surrounding tissue. Thus any mechanical vibration that results from energy input into the body will cause relative motion between the electrode and the surrounding tissue, again with the attendant risk of shearing or abrasion of the surrounding tissue.

Electrodes made to have a high degree of compliance are known. A problem with such structures is that they are limited in the manner in which they can interact with a particular tissue. More specifically, such highly flexible electrodes cannot be inserted into tissue because the flexible electrode itself does not have the necessary mechanical stiffness for it to be pushed into the cellular matrix of a given tissue. These devices can only be affixed to the surfaces of a tissue or inserted into a bodily organ that has a hollow cavity, such as the surface of the cochlear membrane, which will allow insertion of the flexible structure.

SUMMARY OF THE INVENTION

In a first aspect, the present invention comprises an electrode array having a substantially planar electrode body supporting one or more electrodes. Each of the electrodes comprises an electrode pad at its lower end, a connector pad at its upper end, and a conductor located within the body and electrically connecting the electrode pad and the connector pad. The body has an opening in registry with the electrode pad to the ambient and an opening in registry with the connector pad so as to expose the pads to the ambient.

In another aspect the invention comprises an electrode and an introducer for implanting the recording/stimulating section of the electrode into the tissues of a patient. The introducer has a helical lower portion. The lower end of the electrode is attached to the distal end of the introducer.

In a further aspect of the invention, introducer is used to implant the recording/stimulating section of the electrode into the tissues of a patient. The distal end of a cannula is inserted into the tissues of the patient. The distal end of the introducer is introduced into the cannula. The helical portion of the introducer unwinds to pass through the cannula and reforms into a helix as it exits the lower end of the cannula. The introducer pulls the recording/stimulating section of the electrode along with it to position it in a helical configuration within the tissues of the patient. The introducer is then detached from the electrode and extracted, leaving the electrode in place.

Objects, features, and advantages of the present invention will become apparent upon reading the following specification, when taken in conjunction with the drawings and the appended claims.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT

Referring now to the drawings, in which like numerals indicate like elements throughout the several views,FIGS. 1 and 2illustrate a flexible electrode array10. The electrode array10has an upper end12, a lower end14, a front16, and a back18. The electrode array10comprises an insulating body20and a plurality of electrodes21. Each electrode21comprises a conductor22preferably largely encapsulated inside the insulating body20, an exposed electrode recording/stimulating pad24at the lower end of the body20, and an exposed connector portion or bonding pad25at the upper end of the body. The electrode array10of the disclosed embodiment is 1-100 mm in length, 0.01-0.1 mm in width, and 1-10 microns, preferably approximately 1 micron, in thickness.

With further reference toFIG. 1, the electrode array10can be viewed in terms of its function. When thus considered, the array includes a connector area26adjacent its upper end12, an electrode recording/stimulating section28adjacent its lower end, and a signal conducting region30in its intermediate portion interconnecting the connector area26and the electrode recording/stimulating section28.

For convenience of description the electrode array10depicted in the drawings shows only a single pair of electrodes21. It will be understood that the number of electrodes21is not critical and that a greater or lesser number of electrodes can be provided, depending upon the needs of the particular application.

FIG. 3shows a flexible electrode array10mounted to an introducer32for introducing the electrode recording/stimulating section28of the array10into the tissues of a patient. The introducer32comprises a wire having an upper end33and a lower end34. The wire is preferably formed from a shape memory material such as nitinol. The upper portion35of the introducer32is straight, and a lower portion of the introducer is formed into a helix36. The electrode array10is adhered to the introducer32by a layer38of a biocompatible, dissolvable adhesive such as mannitol.

FIGS. 4-6illustrate a method of using the introducer32for placement of the electrode recording/stimulating section28of the flexible electrode array10into the body of a patient. Referring first toFIG. 4, a cannula40is inserted into the tissues42of a patient. The cannula has an upper end44and a lower end46. To minimize trauma to the tissue42, the cannula40can be of a diameter smaller than the diameter of the helix36of the introducer32. As shown inFIG. 5, with the electrode array10attached to the helical introducer32, the lower end34of the introducer is inserted into the upper end44of the cannula40, and the introducer32is then rotated in the direction of the helix36. This rotation causes the helix36with electrode array10attached thereto to unwind as it advances within the cannula40. As the lower end34of the introducer32emerges from the lower end46of the cannula40, the shape memory material of the introducer32causes the helix36with attached electrode array10to resume its coiled configuration within the tissues42of the patient.

FIG. 6shows the introducer32and attached electrode array10with the helical portion36fully coiled within the tissues42of the patient. The upper end33of the introducer protrudes from the upper end44of the cannula40.

After a period of exposure to fluid within the tissues, the adhesive layer coupling the electrode array10to the introducer32dissolves. Then, as shown inFIG. 7, the introducer32can be rotated in the direction opposite to the turns of the helix36to withdraw the introducer from the patient, leaving the electrode array10in place.FIG. 8shows the introducer32fully withdrawn from the cannula40. The cannula40can now be withdrawn, leaving the electrode recording/stimulating section28of the electrode array10coiled within the tissues of the patient.

FIG. 9illustrates an alternate arrangement of the electrode array10and introducer32. Rather than attaching the electrode array10to the introducer32along the entire length of the helical section36, the electrode10is attached only at the tip34of the introducer. Attachment can be made by a dissolvable adhesive, as previously explained, or by a suitable one-way mechanical connection that will pull the electrode in a first direction but disengage when the introducer is moved in the opposite direction. When the introducer32is helically advanced into the tissues of a patient, the helical portion36of the introducer will create a helical track within the tissues. The electrode array10is too flexible to make its own track and will thus follow the tip34along the helical track created by the introducer. When the introducer32is subsequently backed out of the tissue, the electrode array10will remain in place.

FIGS. 10-12illustrate an alternate embodiment of an electrode array50. The electrode array50comprises an insulating body52having a first section54and a second section56extending laterally from the lower end58the first section54. The insulating body52has an upper end60, a front62, and a back64. The electrode array50comprises a pair of electrodes65. Each electrode65comprises a conductor66preferably at least largely encapsulated inside the first section54of the body52. Each electrode65further comprises an exposed electrode element68extending along the second section56of the insulating body52. A conducting gap70is formed in the second section56of the body52between each adjacent pair of electrode elements68. Exposed connector portions or bonding pads72are provided at the upper end of the body52. The body52between the upper end60and the lower end58is 1-100 mm in length and 0.01-0.1 mm in width. The second section56of the body52of the disclosed embodiment is 0.1 to 1.0 mm in height and 1.0 to 10.0 mm in length. The electrode array50of the disclosed embodiment is 1-10 microns, preferably approximately 1 micron, in thickness.

As with the electrode10, the electrode50can also be defined in terms of its functionality, with a connector area73being located adjacent its upper end60, an electrode recording/stimulating section74adjacent its lower end58, and a signal conducting region75in its intermediate portion interconnecting the connector area73and the electrode recording/stimulating section74.

InFIG. 13the second section56of the insulating body52with exposed electrode elements68(not visible inFIG. 13), also known as the electrode recording/stimulating section74, is wrapped into a cylindrical coil76. This coil76locates the electrode elements68in a three-dimensional matrix. The innermost turn of the coil76is loosely wrapped such that a hole77is formed in the center of the coil.

FIG. 14depicts an assembly80for introducing the coil76of the electrode array50into the tissues of a patient. An electrode array50has its electrode recording/stimulating section wrapped into a cylindrical coil76, as previously described. A guide wire82of indeterminate length extends through the hole77in the center of the coil76. A length of hypodermic tubing88is telescopically disposed over the guide wire. The length of hypodermic tubing88has an outer diameter larger than the hole77in the center of the coil76such that the lower end89of the tubing abuts the upper surface of the coil76.

FIGS. 15-19illustrate a procedure for use of the device80to introduce the coil76of the electrode array50into the tissues90of a patient. Referring first toFIG. 15, the guide wire82is introduced into the tissues90and advanced under appropriate imaging technology until the forward tip92of the guide wire82is located proximate to the target site. A cannula94is then inserted over the guide wire82. The proximal end of the guide wire82is threaded through the hole77in the center of the coil76of the electrode50. The length of hypodermic tubing88is advanced over the proximal end of the guide wire until it abuts the coil76. Thereafter further advancement of the hypodermic tubing88pushes the electrode50along the guide wire82.

As shown inFIG. 16, the hypodermic tubing88is used to advance the electrode array50along the guide wire82until the coil76of the electrode array is located within the target site. At this point, the guide wire82and hypodermic tubing88are removed, as shown inFIGS. 17 and 18, and the cannula94is withdrawn, as shown inFIG. 19, leaving the coil76of the electrode50positioned within the tissues80of the patient. The bonding pads72are disposed outside the patient's body to enable the electrode array50to be electrically connected to external electronics for stimulating or detecting electrical activity within the tissue90.

The purpose of coiling the electrode recording/stimulating section74of the electrode array50into a cylinder is to locate the electrodes in a three-dimensional arrangement, as opposed to the substantially linear arrangement of the electrode recording/stimulating section24of the electrode array10. However, it will be appreciated that other methods of placing the electrode recording/stimulating section24of the electrode array10in a non-linear path may be implemented, such as folding the section24over onto itself a number of times to create a substantially box-shaped array98(seeFIG. 20).

Manufacture of the electrode array10will now be explained with reference toFIGS. 21-37.

InFIG. 21, a substrate110receives a deposited layer of an insulating material112. In the disclosed embodiment, the substrate is glass, quartz, silicon. Also in the disclosed embodiment, the insulating material is polyimide deposited in a layer 200-500 nanometers thick.

InFIG. 22, a layer of conducting material114has been deposited atop the layer of insulating material112. In the disclosed embodiment, the layer of conducting material is gold, platinum, or other noble metal approximately 200-500 nanometers thick.

FIG. 23shows a layer of photoresist material116deposited on top of the layer of conducting material114. In the disclosed embodiment, the photoresist material is deposited in a layer 200 nanometers thick.

Referring now toFIG. 24, an optical mask118comprises a translucent backing sheet120and opaque masking areas122. Openings124are formed in the opaque masking areas122. The optical mask118is positioned above the photoresist layer116. UV light126is then directed onto the optical mask118such that it shines through the openings124in the opaque masking areas122and onto the photoresist layer116beneath.

InFIG. 25, the photoresist layer116has been chemically developed to remove those areas130that have been exposed to the UV light.

InFIG. 26a chemical etching agent is applied onto the chemically developed photoresist layer116. The chemical etching agent etches apertures132in the conducting material114through the apertures130in the developed photoresist layer116. Upon completion of the chemical etching process, the conducting material114is now the finished conductors22.

FIG. 27illustrates that the photoresist layer116has been removed from the top of the conductors22. In the disclosed embodiment the removal is accomplished by placing the assembly in, e.g., acetone.

InFIG. 28, additional insulating material has been deposited onto and around the conductors22to create a layer136that extends above the tops of the conductors. Again, in the disclosed embodiment the insulating material is polyimide.

InFIG. 29, a mask138for plasma etch has been deposited on top of the layer136of insulating material.FIG. 30shows a layer of photoresist140added atop the mask138.

InFIG. 31, an optical mask142comprising a translucent backing sheet144and opaque masking areas146is positioned above the photoresist layer140. UV light is then directed onto the optical mask142such that it shines through the areas between the opaque masking areas146and onto the photoresist layer140beneath.

Referring now toFIG. 32, the photoresist layer140has been chemically developed to remove those areas148that have been exposed to the UV light, thereby exposing selected portions of the insulating layer136.

InFIG. 33, a chemical etching agent has been applied onto the chemically developed photoresist layer140. The chemical etching agent etches the mask for plasma etch142through the apertures148(FIG. 32) in the developed photoresist layer140. Upon completion of the chemical etching process, the mask for plasma etch142comprises apertures150formed therethrough.

InFIG. 34the photoresist layer140(see, e.g.,FIG. 33) has been removed to expose the mask138with apertures150formed therethrough. InFIG. 35, the insulating layer136is etched with plasma through the apertures150in the mask138. This plasma etching process removes selected portions of the insulating layer136to expose the electrodes24and bonding pads25.

InFIG. 36the mask138for plasma etch (see, e.g.,FIG. 34) has been removed to expose the upper surface of the insulating layer136.

FIG. 37shows the finished electrode array10removed from the substrate110.

Unless otherwise stated, terms used herein such as “top,” “bottom,” “upper,” “lower,” “left,” “right,” “front,” “back,” “proximal,” “distal,” and the like are used only for convenience of description and are not intended to limit the invention to any particular orientation.

Finally, it will be understood that the preferred embodiment has been disclosed by way of example, and that other modifications may occur to those skilled in the art without departing from the scope and spirit of the appended claims.