WO2010148378A1

WO2010148378A1 - Lead having polymeric layer disposed over electrode

Info

Publication number: WO2010148378A1
Application number: PCT/US2010/039298
Authority: WO
Inventors: Carl Wahlstrand; Dale Seeley; Gabi Molnar
Original assignee: Medtronic, Inc.
Priority date: 2009-06-19
Filing date: 2010-06-21
Publication date: 2010-12-23

Abstract

An implantable medical lead includes (i) a lead body having a proximal region and a distal region; (ii) an electrical contact disposed at the proximal region; (iii) an electrode disposed at the distal region; and (iv) a polymeric layer disposed over the electrode to prevent the electrode from directly contacting a nerve of a patient when the lead is implanted in a patient. Such a lead may be implanted in a patient such that the polymeric layer is in direct contact with the nerve of the patient.

Description

LEAD HAVING POLYMERIC LAYER DISPOSED OVER ELECTRODE

RELATED APPLICATION

This application claims the benefit of priority to U.S. provisional patent application no. 61/218,448, filed June 19, 2009, which provisional application is incorporated herein by reference to the extent that it does not conflict with the present disclosure.

FIELD

This disclosure relates to implantable medical leads; particularly to implantable medical leads configured to directly contact a nerve of a patient.

BACKGROUND

Many implantable medical devices, such as neurostimulators, pacemakers and defibrillators, transmit electrical signals to provide therapy to a patient. Implantable medical leads deliver signals generated from such devices to tissue of the patient via one or more electrodes of the lead. In some cases, the electrodes are placed adjacent or in contact with a nerve of the patient. Such placement ensures that the generated electrical signals are applied to the intended nerve.

However, direct contact of the electrode(s) with the nerve may result in damage the nerve. Accordingly, physicians often insert fascia tissue of the patient between the electrode and the nerve to minimize nerve damage that may occur over time. Insertion of facia tissue can result in inconsistent therapeutic results. The amount and thickness of the tissue inserted between the electrode and the nerve can vary; the composition of the facia tissue from location-to-location within a patient or from patient-to-patient can vary; etc. BRIEF SUMMARY

The present disclosure describes, among other things, leads having a polymeric layer disposed over an electrode. The polymeric layer can, in a sense, act as a built-in facia layer to separate the electrode from a nerve in situations where the electrode is placed in very close proximity to a nerve (e.g., a cut-down procedure). The composition, thickness and properties of the polymeric layer, unlike facia tissue, can be carefully controlled and thus can serve to not only protect the nerve but also to reduce variability and improve therapeutic effectiveness.

In various embodiments, an implantable medical lead includes a cuff portion and an electrode configured to at least partially wrap around a nerve when implanted. The electrode is positioned in the cuff portion. The lead further includes a polymeric layer disposed over the electrode to prevent the electrode from directly contacting the nerve when implanted. The polymeric layer, when implanted, has a Young's modulus of less than about 5 Mpa and is configured to allow conduction of an electrical signal from the electrode to the nerve. The cuff portion may, in some embodiments, have first and second legs and an interior body portion between the first and second legs. In such embodiments, the electrode is located at the body portion. In such embodiments, the polymeric layer may be disposed over the entire interior body portion or a substantial portion (e.g., 90% or more) thereof.

In some embodiments, an implantable medical lead includes (i) a lead body having a proximal region and a distal region; (ii) an electrical contact disposed at the proximal region; (iii) an electrode disposed at the distal region and operably coupled to the contact; and (iv) a polymeric layer disposed over the electrode to prevent the electrode from directly contacting a nerve of a patient when the lead is implanted in a patient. Such a lead may be implanted in a patient such that the polymeric layer is in direct contact with the nerve of the patient. In some embodiments, the polymeric layer is soft and has Young's modulus, when implanted, of less than about 5MPa. For example, the polymeric layer may comprise silicone or a hydrogel, such as a hydrogel capable of absorbing greater than 50%, or greater than 100%, of its dry weight of water.

In numerous embodiments, a method for implanting a lead is described. The lead has (i) a lead body having a proximal region and a distal region; (ii) an electrical contact disposed at the proximal region; (iii) an electrode disposed at the distal region and operably coupled to the contact; and (iv) a polymeric layer disposed over the electrode to prevent the electrode from directly contacting a nerve of a patient when the lead is implanted in the patient. The method includes placing the lead in the patient such that the polymeric layer directly contacts a nerve of the patient. The electrode may be a cuff electrode and the cuff electrode may be wrapped around at least a portion of the nerve.

These and various other features and advantages will be apparent from a reading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a representative implantable medical system including a generic implantable medical lead.

FIG. 2 is a schematic perspective view of a distal portion of a lead having a cuff electrode wrapped around a nerve.

FIG. 3 is a schematic top view of an embodiment of a lead shown in FIG. 2.

FIG. 4 is a schematic top view of a distal portion of a lead.

FIG. 5 is a schematic top view of a distal portion of a lead.

FIGS. 6A-C are schematic cross-sectional views of embodiments of a portion of the lead depicted in FIG. 3, taken through line 6-6. FIGs. 7A-B are schematic cross-sections of embodiments a lead depicted in FIG. 4, taken through line 7-7.

The drawings are not necessarily to scale. Like numbers used in the figures refer to like components, steps and the like. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. In addition, the use of different numbers to refer to components is not intended to indicate that the different numbered components cannot be the same or similar.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration several specific embodiments of devices, systems and methods. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the devices, systems and methods described herein. The following detailed description, therefore, is not to be taken in a limiting sense.

All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure.

As used in this specification and the appended claims, the singular forms "a", "an", and "the" encompass embodiments having plural referents, unless the content clearly dictates otherwise.

As used in this specification and the appended claims, the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise. As used herein, "representative" and "exemplary" are used in the context of "providing an example" and do not necessarily indicate that the example provided is superior to, or more particularly suited for the intended purpose than, other potential examples.

As used herein, "over", as it relates to the positional relationship of a polymeric layer and an electrode, means that the polymeric layer is disposed relative to the electrode such that the polymeric layer is between the electrode and the tissue to which the electrode is configured to deliver a signal when the electrode is implanted.

The present disclosure describes, inter alia, systems, devices, and methods that employ a lead having a polymeric layer disposed over an electrode. The use of such leads can reduce potential damage to nerves, particularly when the electrode is implanted in close proximity to the nerve, and may improve therapeutic efficacy by reducing variability associated with traditional fascia tissue methods for separating a nerve from an electrode.

The teachings presented herein are applicable to any implantable medical device system employing an electrode for delivering electrical signals to or receiving signals from a tissue of a patient. For example, the system may include a neurostimulator, such as a peripheral nerve stimulator, a spinal cord stimulator, or a deep brain stimulator; a cardiac pacemaker or defibrillator; a gastric stimulator; a monitoring device; or the like.

Referring to FIG. 1, a schematic side view of an embodiment of a representative system 100 is shown. The system 100 includes an implantable electrical signal generator 10, a lead extension 30 and a lead 20. Implantable electrical signal generator 10 includes a connector header 40 configured to receive plug 50 at proximal end of lead extension 30 or other adaptor to couple lead 20 to electrical signal generator 10. The distal end portion of lead extension 30 includes a connector 60 configured to receive proximal end portion of lead 20. Connector 60 includes internal electrical contacts 70 configured to electrically couple extension 30 to lead 20 via electrical contacts 80 disposed on the proximal end portion of lead 20. Electrodes 90 are disposed on distal end portion of lead 20 and are electrically coupled to electrical contacts 80, typically through conductors (not shown). In general, a lead 20 may include any number of electrodes 90, e.g. one, two, three, four, five, six, seven, eight, or sixteen. Typically, each electrode 90 is electrically coupled to a discrete electrical contact 80. While not shown, it will be understood that more than one lead 20 may be operably coupled to one electrical signal generator 10 or one extension 30 or that more than one extension 30 may be operably coupled to one electrical signal generator 10. It will be further understood that lead 20 may be coupled to electrical signal generator 10 without use of extension 30 or adaptor.

Any lead may include a polymeric layer disposed over an electrode in accordance with the teachings provided herein. When an electrode is configured to be placed in close proximity to a nerve, it may be desirable to employ a lead having a polymeric layer disposed over the electrode as discussed herein. In many embodiments, the lead is implanted such that the polymeric layer is in direct contact with the nerve. The polymeric layer can serve to protect the nerve from problems associated with direct contact of the electrode with the nerve. While it is not necessary for a lead having a polymeric layer over an electrode as discussed herein to be employed in close proximity to a nerve, the discussion presented herein is directed to such uses for the sake of brevity.

Examples of leads that may be used in applications where an electrode is adjacent a nerve are depicted in FIGS. 2-5 (only distal portions of the leads are shown). Referring now to FIGS. 2-3, embodiments of a lead 20 having a cuff electrode 90 are shown. The distal portion 28 of the lead 20 may contain a plurality of electrodes 90, 90' that are configured to wrap around a nerve 200. The cuff distal portion 28 in the depicted embodiment is semi-cylindrical or U-shaped providing for a half-cuff. Of course, the cuff distal portion may be a full cuff, a three quarter cuff, or the like. Once wrapped around the nerve 200, the cuff distal portion 28 may be sutured around the nerve 200 or otherwise held in place around the nerve. The electrodes 90, 90' may be employed in any suitable configuration. For example, electrode 90' may be configured to be an active electrode and electrodes 90 may be configured to be current guarding electrodes. In the embodiments depicted in FIGS. 2-3, the distal cuff portion 28 includes first 282 and second 284 legs and an interior body portion 286 between the legs 282, 284. The bodies of the legs 282, 284 and the interior body portion 286 are formed from electrically insulating material. The electrodes 90, 90' are formed from electrically conductive material, such as platinum. Conductors (not shown), such as insulated MP- 35N wires, run through the lead body 25 and into the first leg 282, where they are electrically coupled with the electrodes 90, 90' such as by welding, soldering, or the like.

Referring now to FIGS. 4-5, leads as described herein may be surgical or percutaneous leads. As shown in FIG. 4, a lead may include a paddle shaped distal portion 28 containing electrodes 90. Such paddle shaped leads are often referred to as surgical leads. Examples of surgical leads that may be used or modified to form leads as described herein include Medtronic Inc.'s Resume, SymMix, On-Point, or Specify series of leads. Surgical leads typically contain electrodes that are exposed through one face of the paddle, providing directional stimulation. As shown in FIG. 5, the lead may include a distal portion 28 that includes electrodes 90 that are generally cylindrically shaped. Such leads are often referred to percutaneous leads. Examples of percutaneous leads that may be used or modified to form leads as described herein include Medtronic Inc.'s Quad Plus, Pisces Quad, Pisces Quad Compact, or 1x8 SubCompact, 1x8 Compact, and 1x8 Standard leads. Such percutaneous leads typically contain ring electrodes that apply an electrical stimulation signal to tissue in all directions around the ring. Surgical or percutaneous leads may be implanted in any suitable location of a patient, such as adjacent a nerve, so that electrodes 90 can apply an electrical signal to a target tissue.

Referring now to FIGS. 6A-C, schematic cross-sectional views of embodiments of a distal portion of a lead as depicted in FIG. 3, taken through lines 6-6, are shown. In the embodiment depicted in FIG. 6A, a separate polymeric layer 300 is disposed over each electrode 90, 90'. In the embodiment, depicted in FIG. 6B, a polymeric layer 300 is disposed over more than one electrode 90, 90' (in this case, all three of the electrodes) and intervening portions of the lead body 21 surrounding the electrodes. In the embodiment depicted in FIG. 6C, the polymeric layer 300 is disposed over an entire surface of the distal portion of the lead, including all of the electrodes 90, 90'. The surface of the lead over which the polymer layer 300 is disposed is the surface that is intended to contact the nerve, or be placed in close proximity to the nerve, when the lead is implanted in the patient. Thus, the polymeric layer 300 rather than the electrode 90, 90' will contact the nerve or tissue near the nerve. In some embodiments, the polymeric layer 300 will also serve as a buffer between the lead body 21 and the nerve or nearby tissue.

Referring now to FIGS. 7A-B, schematic cross-sectional views of embodiments of a distal portion of a lead as depicted in FIG. 4, taken through lines 7-7, are shown. In the embodiment depicted in FIG. 7A, the polymeric layer 300 is disposed over the electrode 90, but is not disposed over the lead body 21. In the embodiment depicted in FIG. 7B, the polymeric layer 300 extends over at least a portion of the lead body 21. It will be understood that the embodiments depicted in FIGS. 6-7 are merely representative of how a polymeric layer 300 may be disposed over an electrode 90 or lead body 21, and that the polymeric layer 300 may cover any portion or all of a surface of an electrode 90 or lead body 21.

In various embodiments, a polymeric layer is disposed over one or more electrodes of a lead. In some embodiments, a polymeric layer is disposed over each of the electrodes of a lead. In many embodiments a polymeric layer is disposed over all of the electrodes of a lead. The polymeric layer may be disposed over all or a portion of an electrode that would otherwise be exposed through the lead (and configured to directly contact tissue of a patient when implanted). In many embodiments, the polymeric layer covers the entire surface of the electrode. The polymeric layer may further extend over at least a portion of a surface of the lead body. In some embodiments, the polymeric layer extends over substantially all (e.g. 95% or more) of a surface (e.g., the surface through which an electrode is exposed in a surgical lead - see, e.g., FIG. 4) of a lead body. In many embodiments, a polymeric layer is disposed on a surface of the lead that is intended to come into contact with, or to be placed adjacent a nerve (e.g., the distal portion of the lead that contains the electrodes). The polymeric layer may be in the form of a tube, jacket, sheath, sleeve, cover, coating, or the like. The polymeric layer may be extruded, molded, coated on, grafted to, embedded within, adsorbed to, bonded or adhered to, etc., the surface of the electrode or lead body.

The polymeric layer may be formed of any suitable material capable of allowing the electrode to maintain electrical communication with tissue of the patient when the lead is implanted in a patient or subject. Depending on the composition and nature of the polymeric layer, the thickness of the layer may vary. For example, if the polymeric layer is formed from a more electrically insulating material, the layer will generally be thinner than if formed from a less electrically insulating material. In many embodiments, the layer has a thickness of 2 mm or less. In some embodiments, the layer has a thickness of 0.5 mm or less. Of course, it will be understood that other thickness may be used, and the composition of the layer varied to ensure desired electrical characteristics.

The size and numbers of pores in the layer can also affect the desired thickness of the polymeric layer. For example, more pores and larger pores may allow for a thicker polymeric layer than less and smaller pores, as bodily fluid may pass through or fill the pores and provide electrical conductivity. In various embodiments the layer has an average pore size of 1 mm or less. In some embodiments, the layer has an average pore size of 50 micrometers or less, such as between about 5 micrometers and about 50 micrometers. It will be understood that the layer may contain a mixture of smaller pores and larger pores. In such cases, the number of smaller holes may be greater than the number of larger holes. Of course, the layer may have any suitable number and size of pores.

Generally, the polymeric layer when implanted (taking into account that bodily fluid may be conductive) should provide local conductivity. That is, electrical current near the electrode should pass straight across polymeric layer and not uniformly distribute the charge over a large area. However, in some circumstances, it may be desirable for the polymeric layer to distribute the charge over large area (e.g., over the entire surface of the polymeric composition).

In addition to being able to allow conductance of electrical signals, the polymeric layer is configured to provide a soft (relative to an electrode) layer to be placed against a nerve. In many embodiments, the polymeric layer has a stiffness (e.g., Young's modulus) that is similar to that of facia that may surround the nerve of interest. While it is often difficult to precisely determine the stiffness of facia tissue, it is believed that if the polymeric layer has a Young's modulus of 50 MPa or less it may be sufficiently soft to avoid undesired harm or damage to a nerve. For example, the polymeric layer may have a Young's modulus of 20 MPa or less, 10 MPa or less, 5 MPa or less, or 2 MPa or less, when implanted. For example, the layer may have a Young's modulus of between about 0.1 MPa and about 2 MPa when implanted.

For many suitable polymeric materials, it is desirable to know or predict the electrical and mechanical properties when implanted, as they may be different than when stored on a shelf. For example, one suitable type of polymeric material for forming a soft conductive polymeric layer is a hydrogel. Any suitable biocompatible hydrogel may be used. Hydrogels can absorb 50%, 100%, or 200% or more of their dry weight when placed in water. Due in part to their significant water content, hydrogels possess a degree of flexibility similar to natural tissue and can serve as a soft interface between the lead or the electrode and the tissue, preventing damage that might otherwise result from contacting the lead or electrode with a nerve. In addition to imparting a soft surface, a hydrogel layer would also impart desired electrical characteristics when implanted due to the large amount of absorbed water and conductance via bodily fluid.

Any suitable hydrogel may be used to disposed over an electrode, lead or portion thereof. Examples of suitable hydrogels include gelatin, carrageenin, alginic adic, 2- hydroxyehtyl polymethacrylate, polyethylene glycol, polyacrylamide, polyvinyl alcohol, and the like. OF course, many other hydrogels exist and are known in the art.

Of course, other non-hydrogel or non-swellable polymers may be used. Examples of commonly used materials that may be used to form a polymeric layer include organic polymers such as silicones, polyamines, polystyrene, polyurethane, acrylates, polysilanes, polysulfone, methoxysilanes, and the like. Other polymers that may be utilized include polyolefins, polyisobutylene and ethylene-alphaolefin copolymers; acrylic polymers and copolymers, ethylene-covinylacetate, polybutylmethacrylate; vinyl halide polymers and copolymers, such as polyvinyl chloride; polyvinyl ethers, such as polyvinyl methyl ether; polyvinylidene halides, such as polyvinylidene fluoride and polyvinylidene chloride; polyacrylonitrile, polyvinyl ketones; polyvinyl aromatics, such as polystyrene, polyvinyl esters, such as polyvinyl acetate; copolymers of vinyl monomers with each other and olefins, such as ethylene-methyl methacrylate copolymers, acrylonitrile-styrene copolymers, ABS resins, and ethylene-vinyl acetate copolymers; polyamides, such as Nylon 66 and polycaprolactam; polycarbonates; polyoxymethylenes; polyimides; polyethers; epoxy resins; polyurethanes; rayon; rayon- triacetate; cellulose; cellulose acetate, cellulose butyrate; cellulose acetate butyrate; cellophane; cellulose nitrate; cellulose propionate; cellulose ethers; carboxymethyl cellulose; polyphenyleneoxide; and polytetrafluoroethylene (PTFE).

The polymeric layer may be porous, or may be made porous. Porous materials known in the art include those disclosed in U.S. Pat. No. 5,609,629 (Fearnot et al.) and U.S. Pat. No. 5,591,227 (Dinh et al.). Typically polymers are non-porous. However, non- porous polymers may be made porous through known or developed techniques, such as extruding with CO₂, by foaming the polymeric material prior to extrusion or coating, or introducing and then removing a porogen. Non-limiting examples of porogens include salts, such as sodium bicarbonate, gelatin beads, sugar crystals, polymeric microparticles, and the like. One or more porogen may be incorporated into a polymer prior to curing or setting. The polymer may then be cured or set, and the porogen may be extracted with an appropriate solvent. Pores generated by such techniques or processes typically range in size from between about 0.01 micrometer to about 100 micrometer. The size and degree of porosity of polymeric material may be controlled by the size and concentration of porogen used, the extent of mixing with gas or foaming, etc. Accordingly, the conductivity (via bodily tissue) of the polymeric layer may be controlled by varying the conditions under which pores are generated, as pore size and degree of porosity are related to conductivity via bodily tissue. Depending upon the type of materials used to form the polymeric layer, the polymeric layer may be applied to the surface of an electrode or lead body through any suitable process. One method includes directly bonding polymeric layer to the surface. By directly attaching a polymeric layer to the surface of the electrode or lead body, covalent chemical bonding techniques may be utilized. The surfaces may possess chemical functional groups, such as carbonyl groups, primary amines, hydroxyl groups, or silane groups which may form strong, chemical bonds with similar groups on polymeric layer utilized. In the absence of such chemical forming functional group, known techniques may be utilized to activate a material's surface. Surface activation is a process of generating, or producing reactive chemical functional groups using chemical or physical techniques such as, but not limited to, ionization, heating, photochemical activation, oxidizing acids, sintering, physical vapor deposition, chemical vapor deposition, and etching with strong organic solvents. Alternatively, the polymeric layer may be indirectly bound to the surface of the electrode or lead body through intermolecular attractions such as ionic or Van der Waals forces. Of course, if the polymeric layer is in the form of a jacket, sheath, sleeve, cover, or the like, the chemical interaction between the polymeric layer and the surface of the electrode or lead body may be minimal.

Thus, embodiments of a LEAD HAVING POLYMERIC LAYER DISPOSED OVER ELECTRODE are disclosed. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.

Claims

What is claimed is:

1. An implantable medical lead comprising: a cuff portion; an electrode configured to at least partially wrap around a nerve when implanted, the electrode positioned in the cuff portion; and a polymeric layer disposed over the electrode to prevent the electrode from directly contacting the nerve when implanted, wherein the polymeric layer, when implanted, has a Young's modulus of 5 MPa or less and is configured to allow conduction of an electrical signal from the electrode to the nerve.

2. A lead according to claim 1, wherein the cuff portion comprises first and second legs and an interior body portion between the first and second legs, wherein the electrode is located at the body portion, wherein the polymeric layer is disposed over the interior body portion.

3. A lead according to claim 1 or 2, wherein the polymeric layer is capable of absorbing greater than 50% of its dry weight of water.

4. A lead according to claim 1 or 2, wherein the polymeric layer is capable of absorbing greater than 100% of its dry weight of water.

5. A lead according to claim 1 or 2, wherein the polymeric layer comprises silicone.

6. A lead according to claim 5, wherein the polymeric layer comprises pores.

7. A lead according to any of claims 1-6, wherein the polymeric layer has a thickness of 500 micrometers or less.

8. An implantable medical lead comprising: a lead body having a proximal region and a distal region; an electrical contact disposed at the proximal region; an electrode disposed at the distal region and operably coupled to the contact; and a polymeric layer disposed over the electrode to prevent the electrode from directly contacting a nerve of a patient when the lead is implanted in the patient.

9. A lead according to claim 8, wherein the polymeric layer comprises pores.

10. A lead according to claims 8 or 9, wherein the polymeric layer has a thickness of 500 micrometers or less.

11. A lead according to any of claims 8- 10, wherein the polymeric layer is silicone.

12. A lead according to claim 8, wherein the polymeric layer comprises a hydrogel.

13. A lead according to any of claims 8-12, wherein the polymeric layer has a Young's modulus of 5MPa or less when implanted.

14. A lead according to any of claims 8-13, wherein the polymeric layer is disposed over at least a portion of the distal portion of the lead body.

15. A method for implanting in a patient a lead having (i) a lead body having a proximal region and a distal region; (ii) an electrical contact disposed at the proximal region; (iii) an electrode disposed at the distal region; and (iv) a polymeric layer disposed over the electrode to prevent the electrode from directly contacting a nerve of a patient when the lead is implanted in the patient, the method comprising: placing the lead in the patient such that the polymeric layer directly contacts a nerve of the patient.

16. A method according to claim 15, wherein the electrode is a cuff electrode and wherein the cuff electrode is wrapped around at least a portion of the nerve.